Ive sold a number of my machines over the years locally, and always tell the buyer (unless they are a complete nob with a bad attitude) that if anythigns happens over the next 3 months i'm more than happy to drop over to their place and show them how to repair - i've also stated that if its a board problem (or DMD dies - unlikely) i'll do my best to fix it for the cost of parts (normally only a few $$$) but may have to send it away, in which case they will bear the cost.

I'm not a really good selller, as i always try to highlight the bad parts of the machine....

The only time i walked away from a repair from one i had sold was a shady character who wasn't around when i started the repair (his machine was in an outside bar area), and i discovered a sock with a bag inside with 'salt' (according to him!), it looked white and powdery, but i don't think it was salt....