As humans, we’re wired to show gratitude. Someone blesses you for sneezing, and you thank them automatically. A neighbor shovels your walk, and you give them a gift card in return (or cookies, if you’re the baking type).

The point is, at a very basic level we’re uncomfortable when we feel indebted and happier when we settle up. And this phenomenon can benefit your business, too. It’s called reciprocity marketing, and if you understand it you can turn casual customers into loyal and profitable ones.

Here are five tips for going about it:

Give when it’s not expected

An unexpected gift is a welcome surprise. It catches customers off guard and is usually truly appreciated. So, at a time when they least expect it, throw in something free. Or give a discount without the coupon. If circumstances allow, let a customer stay after closing for some solo, private shopping. The more spontaneous the gift, the more pleasant the surprise.

Make it valuable in the customer’s eyes

Think about what makes your customers tick and remember that value is relative. A free dessert may cost your restaurant pennies, but could mean everything to a customer. An extra round of mini golf costs you nothing, but could lead to priceless memories for repeat customers. The point is, you don’t have to give a lot to get a lot in return.

But don’t give away the farm

Like every other tactic, treat reciprocity marketing like a line item and set off an amount for it that fits into your overall marketing budget. Free desserts or rounds of mini golf shouldn’t break you, but they could put a dent in your profits if you don’t keep an eye out. Make sure everyone knows what the limits are so your business can stick to them.

Don’t expect anything in return (it will happen organically)

Ironically, reciprocity marketing works best when you don’t expect anything in return. Think of it as the pot of water that boils best when you’re not paying attention. It will pick up steam eventually. Keep in mind that everyone has a different breakthrough threshold. Some customers will reward you immediately, while others may take longer.

Leave monetizing to other tactics

Reciprocity marketing is hard to monetize because it’s random and unpredictable. While you can try to figure out how much it’s impacting your bottom line, you’ll have more success measuring things like email marketing, direct mail and other traditional tactics. It’s not to say that you can’t try, however. One simple way is to measure lift: the difference in sales before and after you started giving. You might also try surveying your customers over the same periods to measure their attitudes toward your business.

If your business is looking for new ways to succeed, an old proverb sums up reciprocity marketing best: “Give and you shall receive.”