By now, you know that not everything your Facebook friends post online is true. No, Mark Zuckerberg won’t give you a slice of his fortune if you copy and paste your sister-in-law’s status, and no, you won’t get a gift card from the Olive Garden for tagging five friends in the comments.

However, while we all realize that we should cast a skeptical eye on offers that seem too good to be true, fewer of us are as cautious when it comes to posts warning us about situations that seem just scary enough to be credible. Recently, for example, a post swept my feed warning of a growing scam in which cashiers at major retailers add cash back requests to transactions without customers’ approval, then pocket the extra money.

The problem? It just isn’t true.

Shoppers who regularly pay by debit card know that almost all payment terminals require consumers to enter their own cash back requests and then confirm the total charge. Cashiers, in the vast majority of cases, have no access to this interface. Urban myth investigation website snopes.com confirms, arguing that the rumor probably got started when a customer misunderstood the debit card process.

More recently, a video went viral claiming the popular Milk-Bone brand of dog biscuits contains a preservative that causes cancer in dogs. The chemical in question, however, is generally recognized as safe by the Food and Drug Administration, and the alerts failed to link to any actual evidence of carcinogens in the doggie treats.

So before acting on these kinds of warnings, do your own research, however brief. Ask whether there is any evidence that the threat is credible: Have any police issued warnings about the cash-back scammers? Or is the only proof the anecdote of an online friend of a friend? Is there any science cited to confirm the dangers of the product?

If the answer is no, please continue with your old shopping habits. Yes, it feels more responsible to avoid even potential perils. This attitude, however, can lead us to financial foolishness as we avoid stores with good bargains or switch to more expensive brands, just in case.

In this age of rampant social media, it is essential to make sure your consumer savvy runs both ways, side-stepping the real hazards and developing the confidence to decide when you can forge safely ahead.

Have a consumer question or complaint? Reach Sarah Shemkus at seshemkus@gmail.com.