You may already be putting yourself at risk.

As a shopper who loves to save money, I know how easy it is to find loopholes in Costco's membership program. Recently, I discovered a hack that lets curious shoppers enjoy all the splendor of Costco's bulk prices without actually forking over the cash for a membership. But even I can recognize a line that shouldn’t be crossed (like, ahem, fraudulent returns).

Costco's return policy states that they "guarantee your satisfaction on every product" and will offer you a full refund with these rules in mind: electronics have to come back in 90 days, diamonds must be returned within 48 hours, and custom items—as well as alcohol and tobacco products—are not eligible for returns.

However, there are no limits on when and how you can return products—much like other "quality" guarantees made by supermarkets, this means shoppers could theoretically game the system and return perfectly fine items that have already been enjoyed to cash in on free product.

Which is exactly what some members have been doing, according to a new report from Business Insider. There are stories of shoppers who have essentially enjoyed free products by returning already-used items—like an empty bottle of wine, and even a dead Christmas tree in January.

If you're thinking of cashing in on Costco's return policy—or if you've been slyly returning products you've already enjoyed—you should know that Costco has the power to process a return on your membership, too. And it's common knowledge that Costco has previously blacklisted certain shoppers from ever purchasing a membership again.

“In the event a member is not satisfied with Costco merchandise, the membership fees may be refunded and the membership canceled. This decision is made on a case-by-case basis and is at the discretion of each location manager. Additionally, memberships may be canceled due to abuse of the Member Privileges and Conditions,” a Costco spokesperson told Business Insider.

Thinking of purchasing a Costco membership? Read on:

Maryam Nicksolat, who has held a Costco membership since 2006, told Business Insider how she was banished from her local Costco after trying to return a printer she initially purchased in 2010.

Credit: Victor J. Blue—Bloomberg via Getty Images

According to Nicksolat, she discovered issues with the printer after unboxing it, but didn't actually bring it back to the store until recently. When she tried to return it, Costco managers pulled up her account history and said she couldn't return it due to her pattern of rather frequent returns.

Nicksolat eventually got the attention of Jeff Long, Costco's senior vice president of Northeast operations, who wrote her a letter explaining why Costco would be revoking her membership. Business Insider had a chance to look at the letter, and said that Long did refund Nicksolat for the printer and ink she purchased, as well as annual membership fees.

“It is apparent from a review of your membership account that you are not happy with the products you have purchased from Costco, and we are unable to satisfy you as a member,” the letter reads.

Here’s the thing: Returning the occasional item to Costco definitely isn’t a crime (in fact, it’s totally normal and expected), but if you’re worried about putting your membership at risk, read up on the return policy so you don’t get flagged.