It's as much a part of the holiday as the tree: Every year, sometime between Dec. 25 and Jan. 1, you sort through all the random stuff you received, cull the crap, trot around to a handful of stores to make some returns and walk away with a fat stack of cash. Well, they're onto you. OK, maybe not so much you, but people who find ways to amp up their holiday returns.

Fraudulent returns are projected to cost the retail industry a whopping $3.68 billion this holiday season, up 34.3 percent from last year's $2.74 billion, according to the National Retail Federation. For the year, fraud will cost retailers $13.95 billion, up a staggering 45.5 percent from $9.59 billion in 2009.

The NRF says they don't know why retail fraud is on the rise. (Hint: People are still broke.) But some stores plan to tighten up their return policies this year.

Many retailers have open-door policies on holiday returns -- you show up with the merch, they fork over the cash. But you already know that. So do a lot of people. And some of those people take advantage of that in underhanded ways -- from returning stuff they bought for less at other stores to out-and-out reselling stolen merchandise.

Keep reading for some of the more popular scams.

In fact, the "return" of stolen merchandise is the most common type of holiday retail fraud. Let's say Larry buys a box of hot iPhones from Billy (and you don't want to know where Billy got them). Larry then takes a single iPhone to each of several local stores he knows do holiday returns sans receipts: "Gift from Grandma, she just doesn't understand me." Bajinga! A full 93.5 percent of all U.S. retailers say they have been taken in by such scams in the last 12 months.

Other problematic areas include employee-return scams (88.8 percent of retailers reported at least one incident in the last year), the return of stuff bought with fake or hot gift cards or certificates (68.2 percent) and using counterfeit receipts to return merchandise (35.5%).

As a result of rampant fraud, seven in 10 retailers (67 percent) now require customers returning merch without a receipt to show identification. One in five (21.1 percent) require shoppers with a receipt to show ID. While the majority of retailers' policies will remain unchanged this year (83.6 percent), 5.5 percent of retailers say they will actually tempt fate and loosen their holiday return policies (game on!), whereas 10.9 percent say they'll tighten up.

So, if you've been making your holiday bonus the old-fashioned way -- by stealing it -- you might want to come up with a better scam. We recommend a red suit, a brass bell and a kettle.