So if you pay £1 billion for him, that would make him worth £1 billion would it?
There is such a thing as under or over-paying for things, you know, in the real world. A car might objectively be worth £100, but the seller is your uncle, so you get it for £50 ... but you could sell it for £100, because that's its real market value. Or you could have more money than sense, and pay £200 for the same car ... but your over-paying by £100 does not somehow magically increase its real market value by £100.