Think of all the time and money you spend driving traffic to your website, with the hope of it converting into leads and sales. What if you could tap into an entire pool of potential customers and clients without spending a dime? Referrals are not only the least expensive customers to acquire, but they are also typically the easiest to close.

How significant are referrals? Well, 85 percent of small businesses get customers through word of mouth. You are leaving a lot of revenue on the table if you aren’t attempting to generate referrals. Here are five ways to leverage existing customers and clients to make it rain referrals that I personally use to grow my online-marketing consulting business.

1. Under promise and over deliver.

I always like to under promise and over deliver -- it creates happy clients that rave about you to everyone that will listen. If I told a client that a project would take three weeks to complete and it ended up taking four weeks they would be unhappy. If I said it would take three weeks and I delivered the final product at exactly the three-week mark they would be happy, but they expected it to be completed at that time. If I told them that it would take a month and I deliver in three weeks they are instantly turned into a raving, happy customer.

Related: Potential Referrals Are All Around You. Pay Attention.

I do this for two reasons. First, it’s always smart to account for the unexpected. If my company is doing a website redesign for a client, we work in extra time to account for unexpected events. What if a developer becomes sick and misses a day of work? What if the child of a designer is injured at the school playground and they have to leave early one day?

When you under promise and over deliver your customers are completely satisfied and they turn into instant brand ambassadors that will go out of their way to promote your brand, resulting in referrals.

2. Be 100 percent transparent.

While telling the customer or client what you think he or she wants to hear might get you a quick sale, it’s not going to result in them sending any additional business your way.

In the online-marketing industry there are several companies that will promise the world in order to get a new client. I can’t tell you how many times I’ve had business owners say things along the lines of, “If you can guarantee [insert ridiculous demand here] within 30 days I’ll sign a contract today.” I’m completely transparent with them, and while it’s not what they always want to hear and some end up looking for someone that will make false promises, in the long run this forwardness creates happy clients who tell other business owners about my company.

Complete transparency might slow your short-term gains, but I can promise you that it will greatly amplify your long-term growth and success.

3. Focus on solving the problems and satisfying the needs of your customers.

When you put your focus on the needs your product or service satisfies or the problems it solves, rather than the money, you create loyal brand supporters. Look at Apple and some of its most successful products, such as the iPhone. The company focused on creating an amazing product and the outcome resulted in an army of loyal supporters. If you want proof, find any “What smartphone should I buy?” question posted on social media and watch the supporters try to convince the person to purchase an iPhone.

When I consult with clients I focus on helping grow their businesses. When I turn them into satisfied customers I attract referrals, in additional to my retainer. If I didn’t put as much focus on their satisfaction, the retainer fee would still come in, but it’s the referrals that contribute to my business growth.

Related: 6 Barriers to Referral Success

4. Be thankful (and memorable).

One of the easiest ways to generate “money-in-hand” referrals is to send your customers and clients "Thank You" cards. When you show someone that you are thankful and appreciate of their business it instantly makes them feel good. It’s important to make it personal and show that you put some time and effort into it.

Anyone can fire off a "Thank You" email, but that doesn’t have the same impact a hand-written card does. I’m a big fan of hand-written cards -- I also send them out during the holiday season. I’m not a fan of buying a big box of generic cards. I like to pick out a card specific to each client -- one that reflects his or her personality or will connect to them in some way.

Since I speak to my consulting clients multiple times a week I get a very good feel for their personalities and I also learn enough about their personal interests, so I'm able to pick out a card that really triggers emotions. I like to send one to mark six months and then another one after we have been working together for a full year.

5. Ask for them.

This is the easiest one -- simply ask for referrals.

What’s the worst thing that can happen? They tell you no or that they don’t know anyone who would be interested in your product or service. The best scenario? They hand over a referral on a silver platter, primed and ready to convert. If you have one-on-one communication with your customers and clients then always ask them in person or over the phone -- it’s much harder for them to say no when you ask them directly. It’s much easier to ignore an email, although I have seen many brands see success by including a very subtle, “Love our products? Forward this email to your friends that would love us too!” line at the end of emails.

Do you have any additional tips for generating referrals? If so, share them in the comments section below.

Related: How Airbnb and Dropbox Achieved Tremendous Growth With Referral Marketing