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No, golly. Technically there is no sale (if we apply the strict law of contract and agency). However, emotionally, I have a prat sitting next to me on the sofa saying "He's agreed £10k, you need to sell". Never mind about the ins and outs legally (I have no problem dealing with such things).
What it comes down to is him putting me under pressure to sell the car. I need some good reasons why not (other than the fact that I happen to like it a lot).