He mostly buys old crappy stuff so it's pretty much a visual inspection to check if the bike was taken care of by the owner. Old oil, scratches, dirty filter (if accessible) are just generally a bad sign. Also, if too many things (battery, cables,headlight...) have to be replaced on a 500$ POS, you're probably better off looking for something in slightly better condition. As for the advice, I think I just mis-represented what he said cause I don't really know shit about bikes. The first thing he said when I asked is that there really is no general advice because all bikes are made so differently. And I think your experiences in bikes are vaastly different (As in, he mostly ever owned the older stuff. Filter visible on the outside, spark plugs accessible in 5 minutes. So I think different things come to mind when thinking of a "typical" bike). I guess I'll just shut up about the subject because this is just an argument through the broken telephone of my lack of mechanical knowledge. Ooops. Just asked him and he said he'll take electrical problems any time over re-doing a clutch so that part was just me typing shit wrong.
;-) No harm no foul. It's entirely possible he buys bikes that I would dismiss out of hand because when they're that old, they're either (A) abandoned barn finds or (B) maintained by proud owners whose outsized sense of value over their possessions makes them utterly pointless to negotiate with. My general experience is that if it's old and shitty enough that you can get to the plugs easily, and it isn't being driven daily, the carbs are so full of schmutz and crud that the sucka will never run right. The optimal envelope for a slide-valve carb is so narrow that when you get it out of optimal even a tiny little bit you have a bad time - I improved the fuel economy of the KLR by 10MPG just by tightening the needle valve an eighth of a turn.
Yeah, the cost of owning/having the right to ride here adds up to about 1k/year with only half the year where you can legally ride without snow tires :( not much left for the motorcycle after that. And the better the bike, more expensive it gets. Plating only is 1300$/year if you have more than 400cc! Plus, having done moto mechanic school he finds pretty good deals where he replaces basic cables and the battery or I don't know what he does but never resells at a loss a couple seasons down the line.