Using ad networks like adsense doesn’t prevent you from targeting advertisers directly. In fact, that’s how I started; I searched the net for potential advertisers who advertised products relevant to my content and offered them yearly packages. If you choose this option, bear in mind that you’ll need to provide traffic reports and other site statistics.
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!