I sold a friend of mine a Warwick Corvette Std. 5 in April. He could not afford the entire sum at the time, so I agreed to let him pay me over an undefined period of time. (I bet you already know where this is headed.) As of today, he has not even paid me 1/2 of the agreed amount. It's not that he doesn't want to pay for it, stuff just keeps coming up. He moved into a new place and bought all new furniture and things like that. He is an amazing bassist, and has fallen in love with the instrument, but I cannot buy a particular bass that I want until he pays me. What would you do?