Honestly, there is NO way to tell a reliable engine. Obviously, if you can hear the lifters or see visable smoke, that's a sure-fire sign of porblems. But a beaten bike is difficult to acertain. Especially considering new plastics have become cheaper and cheaper to buy.
For body damage and whatnot, here;s what to look for:
1) Check the bolts holding the plastics on. If they are scratched, then he replaced plastics due to lowside crashes or drops.
2) Check mirrors and turn signals for scratches. They often stay entact during a lowside crash or a drop, but will bend back and retain a few scratches.
For engine conditions: RECEIPTS, RECEIPTS, RECEIPTS!!! Some people like to do their own maintenance. Fine......but they should have receipts for the oil filters, air filters, oil purchases, etc.... Make sure they used MOTORCYCLE oil only. Almost all bikes use a wet clutch, and synthetic oils break down some of the parts in the clutch. The bike will never shift the same after using car or synthetic oil.
Also, I would recommend a smaller sportbike before a cruiser to a newbie. Simply put, you are GOING to make mistakes. It's easier to make mistakes with a 400 lb bike instead of a 700-800 lb bike. Aggreed?

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1988 5.0 notch: Previously never modified!!
SN95 block front and rear seats, Mac catback, BBK off-road H-pipe, Steeda castor camber plates, Steeda lowering springs, Tokico shocks/struts, Alpine/MBQuart/PPI audio mods...