Perhaps I'm being overly cautious but I wouldn't say the main thing is to see if he eats. For me the main thing would be having a vet confirm that whatever damage is there, the act of constriction/feeding won't make it worse on the snake. Personally, I wouldn't feed this snake until a vet confirmed what's going on damagewise with this snake. It's obvious from what you've said that something traumatic occurred during the time this snake was at it's first owner's home. For me figuring out exactly what that injury is and how much actual damage was done, would be my first priority (other than getting it into appropriate housing of course).