I've completely rebuilt one of those from the engine up , and there's not much to go wrong with those. Check for signs of leaks,cases, or where the head meets the cylinder, but you'll always see oily dust in some places, so don't be too worried. Listen to how fast it turns over while trying to start it, it should turn over pretty fast if your battery is healthy. Feel that's it's cold when you get there, and see how much crap he has to go threw starting it, and having it idle nicely. Shouldn't be maybe one stall max.. If everything seems fit so far, just check out the obvious stuff,feel the brakes pedal,levers get hard,lights work,etc..If it idles good, revs good, it's probably good. Bottom line, if he has to fart around to get it running, and stay running , walk away. First thing not right on a Harley, she won't stay running. Multi cyl Jap bikes can usually hide problems, lagging cylinders, out of sync carbs.,plug pilot jets ,bad plugs.etc..