I saw some stuff in a hardware store that is intended for removing scratches form painted surfaces on cars and the like, does anyone have any experience of this or any other ideas?
T-Cut or something similar? It works a treat for polishing guitars.
Depending on how scratched-up the current finish looks, it might be worth going over it again with very fine wet-or-dry paper, used wet. At least 1200 grit (I also use 1500, 2000 and 2500). Then polish with the T-Cut on a soft cloth until you get a shine, then buff off any residue with another clean cloth.
The only question is whether he just dulled the surface of the existing finish, or whether he actually removed a fair bit of finish. It's possible to rub through to bare wood with T-Cut if the finish is very thin.