Originally Posted by RacerOne

The beating up part is great until you find out that the seller bought it at some guys garage sale for $100 and is now trying to flip it on CL for a profit, unaware he truly got a 'steal'. Then you go to jail for battery. Good plan.
Go meet the guy in a public place, bring a couple of friends, tell him the bike is stolen, it is yours and you can prove it. If he balks call the police right then and there. The bike will most likely be yours again.

If you have police officer friend ask them to simply show up at the same time.