I am sorry for your loss.
Just by your description I would venture to guess two heat lamps and an UTH on a 10 gallon tank was probably too hot. Did you check the temperature inside the hide?
Anyway without a necropsy you'll never really know -- since the snake seemed alert and healthy at the show and it wasn't apparent to you that there was something wrong then you can't really blame the seller either. It does seem like he did a fair job at trying to make it right.
Good luck with your new snake.
