I've heard of people getting banned for repeatedly buying and returning high value items. I have a video studio and while building it out I was going through a lot of returns of items that just didn't live up to their product pages' claims. As I was nervous about getting canceled I made sure to call Amazon and the CS rep put a note in my file about why I had a high (like 10%, but of relatively expensive stuff) return rate. She told me she gets asked to do that once in awhile and that she'd never heard of problems once somebody had done that.
I did the same thing recently (bought a bunch of networking / wireless gear and only kept the best one) and I noticed that after the 3rd or 4th return they started charging me a small restocking fee. I think it was related to having too many returns in a short time period.
