I have done HITs from them in the past and never had trouble. Over the past couple of weeks, I have been participating in a study with them that required three surveys at $2 each, with a $2 bonus for completing all three. They emailed me today to let me know that I was one of four people whose answers had somehow deleted after submitting the third part, and that if I would take it again, they would pay me for the third part twice, as well as the promised bonus. I've received payment for the other two surveys and have no reason to suspect they won't follow through. Great requester.