Is buying or selling a bike a LIFE OR DEATH situation?
The answer to the first post is straight forward...Agree to a purchase price and hold the bike for the buyer as promised. If a second buyer calls, tell him he is next in line if the buyer doesn't pitch.
If the bike you are selling is a bargain, then there should be many buyers in line.
If the seller sells it to someone else before the agreed time frame, he or she is a chop and "sorry for you", you lost out on THAT deal. There will be another deal and possibly another chop.
Put on the telly and watch TDF. The anger will pass.