I'd think about his riding priorities…
i.e. What does he want to spend most of the time doing. for example:
1. Descending (aka DHing)
2. Riding uphill or long distances
3. Drops and trail based jumps
5. Doing DJs
6. Riding park
7. Etc etc etc
If his doesn't want to ride long distances or uphill then it'll change the bike completely, as with something to do Djs on and if he is after a Dh only bike then again this will change what he needs, basically buying something that is specialist in one area will limit what it can do in total.
Personally I'd look for an all round 2nd hand Hardtail. Something like a Soul, Stiffee, Chameleon etc…