I used to sell on ebay. Mostly arcade parts. Over 8000 sales. Here is my list of blocked buyers. Some I had problems with, others were just too annoying with demands and some that I considered negative feedback happy. I can say this much. Everything I sold as working was tested and working or was listed as either not tested or tested and not working. Still would always get that one buyer that acted like I was trying to rip them off or was trying to fix a game that was dead with my part and it didn't fix the game so they wanted a refund. Edited my list to to just these two people now.
fartknocker2006, funkychunkymonkey07