answer:Use the bike as a hostage until you get the money owed to you. How much is it? For rent? Do you have any documentation? Does this person have a history of having paid you rent regularly before moving, thus setting a pattern. You have to put the bike in escrow, which means in a safe place where you will not use it. Write a little document and have it witnessed. “You own me $xx.xx for yyy. When you pay, I will return your bike.” The bike is now your security deposit…but you have to treat it as such until this is sorted.