@TjLaZer
I would say that if the guy is willing to compensate you at all it is a good gesture on his part. I see from the auction he offered to insure the item at the buyers discresion.
I would in all fairness figure what it would cost to replace the items and cut it in half.
A3630 CPU card = $30.00 (maybe)
Keyboard = $20.00-$30.00
Top case = ? ($20.00)
Total = $70.00-$80.00 /2 = $35.00-$40.00 from him
If it were me that is how I would break it down, just my thoughts.