You are trying to sell your audio system (an amplifier and speakers) to raise money for an upcoming trip overseas

You are trying to sell your audio system (an amplifier and speakers) to raise money for an upcoming trip overseas. The system works great, and an audiophile friend tells you that if he were in the market for this kind of equipment (which he isn’t), he’d give you $500 for it. A few days later the first potential buyer comes to see the system. The buyer looks it over and asks a few questions about it. You assure the buyer that the system works well. When asked how much, you tell the buyer that you have already had an offer for $500. The buyer purchases the system for $550.