On the 4th of May, I decided to sell some of my junk on ebay. A lot of them sold but then came one item that's giving me problems from one buyer. The auction ended on 4th May and he never paid. I sent an email and he says, "Oh. Sorry. I asked my partner to do it. I'll get it ready". 5 days past and I decided to send another email and he says that he would pay on Monday. Monday has come and gone by and I decided to send another email asking what's going on. Nothing. At this point I decide to give him an ultimatum and sent him another message. Pay before the end of the week or I will give him a negative feedback. I really don't want to believe this to be another "WHOOPS. I HAVE COMPUTER PROBLEMS" and it's unusual since the seller has 200 feedback with 3 negatives from last year. How would you deal in this situation and how can I prevent this next time?