Mechanical Turk operates much like TaskRabbit and GigWalk: it’s a corner online where Amazon gathers tasks to be done, people willing to do them, and people willing to pay for them. On Mechanical Turk, you get to do the oddest jobs you can imagine as an online business idea, made possible by a parallel online universe that runs on hits, visits, surveys, reviews, pins, likes, CPCs, reads, and other metrics. But don’t get too ambitious. The small sums being paid out to human Mechanical Turk users rarely add up to anything seriously substantial, even if you invest most of your spare time into it. It's a better opportunity for internationally-based people with internet access and lower costs of living than in the US. Here’s one person’s account of his former life as a Mechanical Turk talking through how he got started with  this business idea and what the experience was really like.
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!