Well.....being nice, or helpful after the sale can come back and bite you.
I had a situation where I was given a car to put rear brakes in and to sell by some relatives. They lived in a rural area, were in college, and didn't have time to mess with it and just wanted it gone. The deal was I was to put brakes in, sell it, and they would give me half of the sale. Why not right?
I fixed the brakes, and the exhaust and sold it. It was a cheap $600 vehicle that was VERY solid at twice the price and then some. I told the people the whole situation. I was basically contracted to fix what I was told to, and sell it.
The people were thrilled....at first. Then a week later I became married to the vehicle. They called me about this and that. For weeks!!! Started calling me at work, and wanting me to look at this or that for them. I mean seriously people?!? Finally after the third week I had enough and put the kibosh on the whole thing and basically had to be downright mean to the lady and tell her to leave me alone.
As far as the poo I bought for my kids. I don't think the kid was being dishonest as much as he was just some ignorant punk kid and didn't know any better. He must have been all of about 17-18. His mother was really nice and told me to call with any questions or problems I had. I would have liked to bitch a little, but I never have.
What I'm GOING to do when it's perfect, is just send the kid a picture of what the machine he sold me is like now, and tell him what I did to it. It won't get me anywhere, but it will be at least a little F.U. to the kid if he DID try to take me. At least I'll feel better. :-p