Renting a car for your summer road trip? Here's how to avoid the potholes when dealing with rental car companies.

1. "Our cars could use a facelift."
After an exhausting flight to Hawaii last Thanksgiving, the one thing Aveek Datta didn't need was a turkey for a rental car. But National Car Rental issued Datta a Ford Mustang convertible that was so beat-up he spent 10 minutes noting every dent and ding on the damage form. What's worse: A peaceful island drive turned into a nerve-racking afternoon when the car's front right wheel began to rattle. Recalls Datta, "We were worried about the wheel falling off."

A falloff is what many consumers are seeing in rental cars' conditions since the travel industry began reeling last year. While National says it regrets Datta's inconvenience and calls it "uncharacteristic," CNW Marketing Research, an auto research firm, says complaints about the industry's cars have jumped 60% since September. And while most companies insist they're not holding on to cars longer, CNW's research shows agencies keeping cars 10 to 30% longer. If you end up with a wreck, John Frenaye, a travel agent in Annapolis, Md., says the rental firm "should offer you some sort of compensation."

2. "Good luck finding our cheapest rate."
Complaints about rental car conditions aren't the only thing rising. Prices have jumped too. During one week in January, the average rental rate rose more than 25%, then continued to climb $1 a week through mid-March.

Cheap rates are still available -- the problem is finding them. Rental companies change prices more often than airlines change airfares. "Industrywide, there's thousands of rate changes a day," says rental car consultant Neil Abrams. Here's proof: During one hour-long Web search, we found six different rates, between $36.09 and $47.99, for the same midsize Hertz car in Atlanta. (Hertz's explanation: "Our prices are based on supply and demand.")

You can find bargain rates by renting off-airport, where prices can be more than 25% cheaper. Plus, you can often rent off-airport and still return the car to an airport location without paying drop charges. We saved $75 on a three-day Avis reservation by booking at a downtown location, and there was no charge to return the car to the airport.

3. "Our prepaid gas option is a rip-off."
To avoid getting gouged on refueling costs, you've probably considered the prepaid gas option -- it lets you return the car without filling the tank up. Sure it's convenient, but hardly a deal. Unless you've brought the tank back completely empty, you've wasted money: Rental companies never refund you for the gas you didn't use.

In addition, the prepaid rates that rental companies claim are competitive often aren't. We called five locations of five major rental companies and compared their rates with the local daily rate from AAA. More than 60% of the time, the prepaid rate was higher than the AAA rate. In one case, the Alamo location at the Seattle/Tacoma airport charged a rate of $1.69 per gallon; the AAA average was $1.22, 28% lower. Do yourself a favor: Before you get to the counter check out AAA's national gas prices at http://198.6.95.31/index.asp.

4. "We won't help you understand your insurance options..."
Which credit card gives you the best insurance coverage when renting? Don't ask the guy behind the counter. "Our employees are not trained to know what credit cards do and do not cover," says Hertz spokeswoman Paula Stifter.

So you're on your own. Start with Diners Club. It's the only major credit card that offers primary coverage when traveling in the U.S., meaning you won't have to involve your own insurance company or pay deductibles if you're in a wreck. It also gives you the most time to report an accident (90 days) and the longest period for which you're covered (31 days) in the U.S. American Express cards and Visa and MasterCards at gold levels and higher provide secondary collision damage coverage, which kicks in after your personal auto insurance. If you're traveling abroad, check with your own credit card company about your coverage before leaving. In many countries you may not need any additional protection. And one more thing: Urban dwellers who don't own a car should buy the supplemental liability in case they cause injury or damage in an accident.

5. "...and the policies we pitch still won't cover everything."
So the guy behind the counter persuaded you to spend the $10 to $20 a day on the collision damage waiver for that extra peace of mind. Don't get too comfortable. Several loopholes buried in the fine print could negate your coverage. For instance, if you're not wearing your seat belt when you damage a Hertz or Budget rental car, the waiver may amount to nothing. And Hertz, Budget, Avis, Enterprise and Thrifty void the waiver if doors were not locked or keys were left in the car when the car was damaged or stolen.

Some rental contracts also include ambiguous language that could give rental companies leeway to void your policy. For example, Enterprise's contract in Massachusetts excludes the protections of the collision damage waiver if you use the vehicle in an "imprudent manner." Boston attorney John Roddy's firm has filed a suit against Enterprise for writing in this exclusion, contending the language could let Enterprise wiggle out of any claim. "Their contract is illegal, ultimately," Roddy says. (Enterprise spokeswoman Christy Conrad says the contract follows Massachusetts guidelines for companies providing collision damage waivers.)

6. "Some of our upgrades have a surprise in tow."
Why rent a Ford Escort while on vacation when you could be driving in style? Since 1995 sport-utility vehicles have gone from 1 to 12% of all rentals, says CNW's Art Spinella, and last year Hertz began promoting its "Prestige" collection, which includes Jaguars and Land Rovers. But watch out for this pothole if you snap up that luxury upgrade: Most credit card companies' collision damage waivers don't cover high-ticket cars (with American Express, for instance, that means any car worth more than $50,000), and some don't cover full-size SUVs.

Steven Chan learned that lesson the hard way. A Budget rental agent convinced him to upgrade to a Ford Expedition SUV from the full-size car he'd reserved. Chan says the agent told him, "It's so easy to drive." Not quite. Chan scraped the SUV on a wall while pulling into a garage, and Budget charged him $2,500. His credit card company, American Express, didn't cover the Expedition. Chan's auto insurance kicked in for part, but he still owes Budget $500. (Budget Group spokeswoman Jenny Sullivan says Chan could have exchanged the SUV if he felt uncomfortable with its size.)

Don't get talked into unwanted upgrades, and double-check what's covered by your credit card. And one other thing:No major credit card company will cover pickup trucks.

7. "We pass the buck."
these days the list of taxes and fees rental agencies hit you with can be longer than your vacation's itinerary. At Boston's Logan Airport, for example, most customers get stuck with a $10 convention center surcharge, a 5% sales tax and a 10% "concession recovery fee." In the end a $38 rate for a midsize car soars to more than $56. Ouch.

All right, you can deal with the sales tax. But what's a "concession recovery fee"? Essentially, it's the fee a rental company pays to do business at the airport-and you're paying it. While some airports do require customers to pay the fee, we contacted 13 of the busiest airports in the country (including Newark, Orlando and Boston), and none require that the customer be responsible. But when travelers complain about the fee, rental company employees often just blame it on the airport. We called the eight major rental companies' reservation lines to inquire about the concession fee at Minneapolis/St. Paul International Airport, which doesn't mandate that renters pay it. Seven companies told us the airport did. (The one who got it right: Hertz.) Eric Johnson, the airport's concession manager, says it's one thing to allow rental car companies to pass along the fee, but "it's another thing when they tell their customers that the airport is forcing them to charge it."

8. "Don't expect the same services at all our locations."
Ryan mccamy was a diehard fan of Hertz's No. 1 Gold program -- until the day he reached the company's Tampa airport location. The Kansas City, Mo., consultant had to wait 45 minutes because the location didn't offer the counter-bypass perk for elite members. McCamy ended up missing an important business meeting. "It was such a nuisance," he says.

Inconsistencies between rental locations can range from fees to frequent-renter perks. Why the confusion? One reason is that many rental agencies are franchised (Thrifty, for example, is 95% franchised), and services and policies can vary from one franchise to another. Plus, car rental companies acknowledge that different state laws can affect policies.

Some say they don't have complete control over franchises. Hertz's franchises have "access to our policies and procedures, but at the end of the day, it's up to the licensees' discretion," says Stifter. "We can't tell them how to run their business."

9. "We're pulling the plug on a few of our perks."
Unless you're an avid follower of frequent-travel programs, you may have missed the not-so-subtle tinkering rental companies have been doing with their rewards recently. National, for instance, has dropped its discounted gas-price perk. Budget's frequent renters now have to fork over 25% more points for a free rental.

On top of these rollbacks, some renters are getting socked with yet another surcharge -- the frequent-flier tax recovery charge, which recoups the taxes rental car companies pay the government for the "frequent flier" miles they give you. While it's only a few cents a day, such nickel-and-diming irks many frequent travelers. Getting the miles, says Bill Davis, an engineer in Colorado Springs, Colo., "almost isn't worth it. It's a sad commentary on how the travel experience has changed."

To avoid the tax, rent from Budget or Thrifty, which don't charge it. Or ask for hotel points; they're not taxed.

10. "Have a spotty driving record? We'll leave you stranded."
Take a look at your driving record. It may cost you your rental reservation. Most major car rental companies will check driving records in at least some states or locations -- and, if it's unsatisfactory to them, deny you a car. Generally, you could be turned down for such violations as driving under the influence or having a suspended license, but you could also be zapped for simply having a few seat belt violations within the past three years.

Clearly, you can understand why rental companies would want to keep bad drivers out of their cars. What's frustrating is that rental agencies wait to check your record until you're at the counter. How come? For one thing, they want to ensure you're actually picking up the car before they spend money on a search. Also maddening: Some companies do a poor job of warning you about the screen. Budget's Web site tells drivers only that they "must have a safe driving record" without explaining its definition of "safe," and during its online reservation process, Avis doesn't mention that it checks driving records. If you're worried you might have one too many speeding tickets, consider trying Dollar or Enterprise. They don't check driving records at all.