You've seen it on countless commercials. The next time you go shopping, you'll find plenty of pitches using it. But it tricks millions of consumers into buying things they can't afford -- and facing the consequences for years to come.

"Look expensive? Don't worry about it! You can afford the payments."

Get it now
Retailers know that you don't want to wait to buy something. An essential part of their marketing strategy is to create an immediate desire to get your hands on hot items right now. If you need an example, just look at Apple (NASDAQ:AAPL) and its iPhone campaign -- a classic example of building demand for an item before it's even available.

With low-priced merchandise, it's not hard to get you to pull the trigger and buy it now. You might well have the cash in your wallet. If not, the prospect of another few bucks on your credit card won't keep you away from the register.

But with big-ticket purchases, it's tougher to get you to buy. That's where those payment plans come in.

Pay for it later
Now don't get me wrong -- credit is a wonderful tool. Without credit, most people would never be able to buy a home. Plenty of business activity depends on it. For instance, farm equipment companies like Deere & Company (NYSE:DE) and Fiat's (NYSE:FIA) New Holland division wouldn't find many farmers able to pay cash for the tractors they need.

I draw the line, however, when people no longer talk about the actual price of an item at all. Ask a car dealer how much your favorite vehicle would cost, and you're more likely to get a spiel about how you can drive away today for $99 down and $249 a month than a straight answer about the sticker price. Even more modest purchases, such as computers and high-definition televisions, have started to jump on the payment bandwagon.

Many people even make the mistake of thinking that lower payments mean that something is actually cheaper. In reality, you're often getting a much worse deal.

Longer credit terms
The trend among retailers is to get your payments as low as possible. The best way to do that is to extend your payments over a longer period of time. As a result, you can now find car loans with terms of five or six years, whereas it used to be hard to get a loan beyond three years. Forty-year mortgages haven't yet taken off, but they're out there -- and interest-only financing gives you payments that don't put a single penny toward paying down your outstanding balance.

Some retailers even let you avoid making any payments for a period after you buy. Select Comfort (NASDAQ:SCSS), for instance, currently offers 18 months of no payments or interest when you buy certain models of their Sleep Number beds. Furniture companies like Ethan Allen (NYSE:ETH) often have similar deals.

Be careful
The lesson here isn't to avoid debt entirely. If you're planning to buy something anyway, favorable credit terms like no-interest periods can actually put extra money in your pocket. The key, though, is to understand that even if you don't have to pay the full cost of an item right away, you will eventually. And if you can't afford it now, you might not be able to do so when the bill comes due.

So don't let the ugly secret of attractive financing lull you into taking on more debt than you can handle. Armed with the knowledge of how much you can afford to pay, you'll be a lot smarter about buying big-ticket items.

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You can get more information about how credit works in our Credit Center. You can learn how to get better rates, find the best financing, and much more.

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Fool contributor Dan Caplinger tries to avoid buying anything on credit. He doesn't own shares of the companies mentioned in this article. Select Comfort is a Motley Fool Hidden Gems pick. The Fool's disclosure policy won't burn you.