I'd say for our bikes, being much newer, as well as overall mechanical and cosmetic condition, my main concerns would be:
Establishing/verifying ownership history;
If it has clean title - AND, in present owners name;
Any accidents/been dropped;
Maintenance history (includes condition of tires, brakes, chain, etc.);
Where was the bike kept (in garage or outside);
What mods have been done (and, if EFI, does it have appropriate tune).
Oh, and I would not finalize a deal (i.e. hand over cash) on any bike without seeing both the bike and the ownership documents.