Often, what happens is that we run into unscrupulous Internet Marketers (IMs) who have less-than altruistic intentions of extracting money from you rather than helping you to make it. However, this isn't something new. People have been falling for networking marketing, pyramid schemes, and affiliate marketing scams since before the start of the net.
What’s the catch? None, really. Cash back apps act as affiliates for many online merchants, which means that whenever you make a purchase through one of the apps, they get a small commission — but then, they give you a portion of that commission as “cash back”. For example, if I buy a pair of Nike shoes through the Ebates app (or website) and spend $75, Ebates may get a $10 commission but then they’ll pass $7 back to me. It’s basically a way to get sale prices on stuff that isn’t on sale!