Ask HN: What are Mechanical Turk's criteria to be a worker?

I have some extra time and was curious about Amazon Mechanical Turk. I've known about it since its inception but have never used it in any way. I was interested in what sort of menial work was available and how the process worked, and if I made $0.25 a week then that would be nice too.

Alas, I don't meet their requirements as a worker! They quickly rejected my main Amazon account, as well as another attempt from a new email. No recourse, just this very ominous judgment: "Customer Support is unable to change this decision and cannot share insight into invitation criteria."

Is anyone familiar with their criteria or what sort of stuff gets you blackballed?