Before having my own website, I spent time reading websites, newsgroups, bulletin boards and forums about the game, and eventually started trading online. Back before search engines were any good most of my time was spent in particular Magic newsgroups, some that talked strategy, and some that were focused specifically on trading and/or buying and selling cards.
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!