If you’re like me, you probably look up online reviews before you go holiday shopping, make vacation plans, or even hire a plumber. Seeing what other people think can be super helpful in weighing decisions — especially before you fork over your hard-earned money.

But did you know that some people are paid to say good things about a company, product, or service? That means you can’t always know if someone is giving a true and impartial opinion. The law says reviewers should be up front about their connection to a company — but some of them aren’t.

It’s useful to read reviews, but take them with a grain of salt. This holiday season, compare reviews from a variety of sites and trusted sources to make sure you’re getting the whole picture. And check out this video for more helpful tips.