The only problem I've had in 12k miles is a 6 monthly need to have the idle mixture set up by the local dealer. Nothing else. The only item that I have had to replace in that time over and above regular service items is the clutch basket and plates which got a bit sloppy - £300.
Don't cut corners with the servicing and it'll be as reliable as a Japanese bike.
I think talking to the owner will often tell you more than looking at the bike. Is he a cretin or a polishing fanatic?