The value you are given for the Aygo here is likely the trade-in value, which is the money you'd receive from selling it to a dealer who will then list it at a higher price. It is common practice - the car needs to be prepared for sale (which costs money) and the dealer needs to make a profit. Based on the two prices, £9500 for a trade-in value seems fair. If you wanted to sell the car closer to what you paid for it your best bet is to try and sell it privately. There is no law that says a dealer must sell a car at a certain price, it's up to the buyer to do their research.