Just one more point about the car trade-in analogy.... Once the quote for a trade-in vehicle is made, agreed upon and signed for then that is that.  If afterwards the dealer discovers a major problem that requires a lot of money to fix... Then it's the dealerships loss.  They do not chase down the customer and re-quote the trade in value and ask the customer to issue them a check for the difference.  They will just increase the asking price for the next customer based on how far into the car the dealership is at that time.