Like someone mentioned, don't meet at your house.
Always keep the keys on you as well as the ownership. (not on the bike incase they take it).
No test rides - the headaches if something were to happen are something you don't want to experience. (they can watch you ride by as a test)
Deposit is non refundable - let them know that. So many doorknobs think they can simply change their mind and ask for deposits back. Letting them know in advance, saves you some headache. If they want the bike, they provide a non refundable deposit and only get the keys/ownership once your agreed balance is paid in full, not before.
