OP did the right thing only because he offered to wait. Having said that, it was an extremely foolish thing to do and makes no sense at all. Why would one go out of their way to hold off potential buyers in order to preserve a
potential sale for a stranger? You place an ad in order to generate as much interest as possible in order to leverage that interest into the best possible offer, then you negate the entire process by telling everyone else to wait because some random guy fortuitously called first.