Used bikes

What should I be aware of when purchasing a used bike? I am no mechanic but am buying from private seller and would like to know any tips when it comes to buy used that is not hard to identify.  

Looking for a used sportbike, acouple things come to mind to look for immediately.
1. Aftermarket/non-original paint. Usually the first sign a bike has been down.
2. Painted/polished/chrome frame. See above--occassionally, done to customize the bike, USUALLY done to hide damage/marks from straightening.
3. Check pegs/levers/mirrors from signs of droppage. It's AMAZING the number of people who re-paint/put on new clutch covers,etc., to try and cover crash damage, and then FORGET to change the shifter lever/bar-ends,etc.,. And God love them for their ignorance.
4. Be careful w/aftermarket mods/parts. Any idiot can put on a slip-on, so don't worry there. But if there are any serious engine/suspension mods, make sure they were done by a real mechanic, NOT two guys w/a case of PBR and some adjustable wrenches.

Past that, use your judgment. TRY and take a knowledgeable buddy along with you. Even better, sse if they'll let you take the bike to a shop to check out. It's well worth paying for an hour of shop labor to have the bike checked over. And if something just doesn't look or feel right, walk away. Don't let someone try to change your mind, it's your money.  

Thanks for your help sloth. I appreciate your help.