Receiving a mysterious delivery that you didn’t pay for might seem like a little gift from a universe. After all, it might be something useful, and you’re typically under no legal obligation to return mistakenly delivered merchandise. It’s free stuff!

Still, be careful: It might also be what’s known as a “brushing scam.” And while a brushing scam usually doesn’t come with any direct danger to you, there are a lot of reasons you should be concerned if you receive an unexpected freebie at your door.

What’s a brushing scam?

A brushing scam involves an unscrupulous vendor sending you an item you didn’t order, allowing them to create the illusion that you did order it. Do that enough times with enough people, and it’ll look like the item is popular. The vendor can then also write fake reviews in your name—Amazon elevates “verified purchasers” in its reviews, giving them extra weight because it has verified that they actually ordered the item in question. A brushing scam therefore makes fake reviews look doubly legit: Someone actually ordered the item, and that verified purchaser leaves the review.

Because these are shady companies, the stuff they send out is usually not high-quality. They’re often fake luxury brands or low-quality stuff, and the brushing scam helps make it look more legitimate.

Okay, so the stuff might be crap, but it’s free! And you can legally keep it! So what’s the big deal if you’re passively helping scammers get over on unsuspecting customers who think you, a real, reliable person, gave it a good review?

Dangers of brushing scams

There’s typically no harm in keeping something sent to you as part of a brushing scam (although that’s not automatically true). But there are many ways a brushing scam should be a red flag:

Online reputation. Those fake reviews might proliferate, and your name will be associated with a scammy, cheap product. Depending on what the item is, people might be harmed in various ways, and you’d be part of that. The Better Business Bureau strongly advises you to contact the retailer that shipped the package to you and alert them. That can get the fake reviews removed.

Loss of account. Amazon and other online retailers don’t like fake reviews, because it undermines consumer faith in their platform. They may take action against involved accounts—and you might be swept up in those crackdowns even though you weren’t directly involved (after all, if you didn’t contact the retailer about the scam, how would they know?). That could mean seeing your account closed, or (rarely—but not never) getting caught up in lawsuits.

Identity theft. All a scammer needs to make the scam work is your name and address, so simply receiving a mystery package doesn’t mean your life is about to fall apart. But it does mean your basic identity information is out there and being used by scammers—and you have no idea if it’s limited to just your name and address. It could be a sign that your personal information has been compromised much more widely, and you need to take some steps to defend against potential identity theft, including checking your credit reports, changing all your passwords, and scrutinizing your credit card statements.

Requests for payment. Usually, brushing scams come in the form of a box that shows up out of nowhere, and that’s it. The lack of direct cost is what makes this scam seem kind of victimless at first. But these scams sometimes do come with requests for payment in the form of postage due or an invoice that arrives later claiming you now owe the company for the item you never ordered in the first place. But you never have to pay for something you didn’t order—and you don’t have to return it, either.