Well if its not ebay sold, Your clear. LOL.... My gsr civic ran like a dream and anyone can vouch that has seen it. i sold it to a girl, and a week later she says hey i threw a rod, is there anyway we can work something out. UM NO!!! Not to be mean but cmon- Its called the Tail light warranty.... Once he drives off its his problem and you dont see the lights its his problem. Yes there is a feeling of guilt.. But in reality its his problem, the only reason you can be held accountable is if bill sale has some kinda of written agreement about the car maybe not working in the future, but that does not seem to be the case. Kindly explain the situation about how there is noway of buying it back but will gladly look at it or guide him to a place to go and have it looked over. I have ran into these problems before, but anyone will tell the guy who bought it, you should have examined it more. But its your call, legally you are clear. Hopefully you met in a disclosed area not at your house.