Depends on the car…they are a guide. I had a Mondeo Zetec Estate 130TDCi, there weren’t many around, they seemed to be about £1k above book on autotrader in my area, so I priced it optimistically, (£1.5k over book) expecting to reduce the price a week later – it sold the following day for £1k over. He phoned and said it was well over book, I justified why (not many around, similar ones are the same price and an hours drive away) told him I would accept £500 less. He came, he looked, he liked, he tried hard to bargain some more but I stood by the minimum price I told him on the phone, next thing I know the cash is on the table 🙂 I was lucky to sell it so quickly, but it was worth what I sold it for.