This hobby is not for the faint of heart. You talked the guy down but did not try the machine on the spot before taking it? (If I am reading your post correctly) There are plenty of good guys that can try and help trouble shoot it for free. Sometimes you have to pay to have something fixed by a pro if you can't figure it out.
Don't give up. There are going to be plenty of days like this depending of what price and condition you buy stuff at.