Updated

With rents through the roof and decent apartments scarcer than ever in America's top cities, it's understandable that renters might be feeling desperate to find a good deal and fall for one of a growing number of fake "for rent" ads online.

Consider this recent beauty: A "cozy" 15-square-foot, graffiti-filled New York City bathroom was advertised as a "hip artist loft" on Craigslist for $30 a month. In spite of these squalid living conditions, plenty of hopeful tenants replied to the ad. At least, until it was revealed that the ad was a hoax.

And this is hardly an isolated incident: Just a few weeks earlier, a new London rental was posted on Twitter of a bed under a stairwell renting for $750 per month. Only upon further investigation, the Independent and other news outlets concluded that this Harry Potter -- esque rental was just a PR stunt.

These ads for fictional apartments don't just dash renters' hopes and waste their time. Some of these are also bona fide scams that attempt to steal peoples' identities or money -- through a "fee" for a credit check that never occurs, for instance.

And although certain ads can scream to all but the most gullible that they're hoaxes, others can look fairly legit and evade even the most street-wise renter. But even in these cases, there are ways to tell if a "for rent" ad is fake. So here are a few blazing red flags:

No phone number

Even in this day and age when people rarely hop on the horn, rental listings are one place where you will still usually see a phone number listed so you can easily reach a flesh-and-blood person.

"Most 'real' rentals always have a number or a person you can talk to," says Jessica Edwards, a Realtor in Wilmington, NC. "The biggest warning flag we typically see in fake ads is no phone contact. The post will have an email but not have a number to contact, or the number does not work."

A funky email

If you do contact a listing and get an email back that looks light years from a real name -- like, say, "mxyzptlk" -- that should give you pause. According to the Consumerist, this could mean this is an auto-generated email account that makes the sleazy scammer behind it harder to track down.

A request for cash upfront

So someone responds to your request and is happy to show you the apartment, that is, as soon as you cough up $50 for a credit check.

"Anytime they ask for any kind of deposit or fee upfront, sometimes before getting into the property, that is also a telltale sign an ad is fake," says Edwards.

Lack of specifics

So an apartment sounds great, but where is it? If some key info is missing -- photos of the room, its address or neighborhood, landlord's name -- then that could be because it doesn't exist.

"One bad sign is if the owner is overseas," says Wendy Flynn, a Century 21 real estate agent in Hesperia, CA, "and needs you to wire funds before you can see the property or mail you the keys." Um, no.

Terms that seem too good to be true

With rent, you usually get what you pay for, so if an ad is hawking what seems like a ridiculously good deal -- the rent is surprisingly low for the area, the landlord is hunky-dory with your paying your deposit in installments or smoking inside -- odds are, there's a catch. Keep your BS detector on high.