Perhaps, like me, you ARE an affiliate. Each pays anywhere from one cent on up to affiliates, like me. It's a form of advertising. I like PlugInGo because it's easy to navigate the website, and easy for me, as an affiliate, to sign up. In addition, PlugInGo gives out all sorts of extra bonus points.
Merchants have to pay for advertising, no matter what.
I have not checked all the prices, but I really like the folks at PlugInGo . I would look into what PlugInGo offers before deciding on which program to join.