I understand market value, you quoted my post where I gave the definition - “the amount for which something can be sold on any given market”. You’re just describing negotiations.
In your Clarke example, if United start at £1.5m and won’t go below £1m, but no buyer will go above the starting offer of £500k, then what’s his market value? Surely it’s £500k because no one is willing to go higher?
Quoting a definition does not prove you understand something, I wasn't describing negotiations.
If hypothetically, United won't go below £1m, and no buyer is willing to pay more than £500k then he's been priced out and essentially there is no market for him, and thus no real market value - just a range between the 2 clubs valuations.
I'll give you another example, in La Liga, where the figures are easier because they're predetermined as a buyout clause:
Messi is indispensable to Barcelona, and so in his contract, he has a minimum release fee clause of €700m or £618m.
There is a market for Messi, in a sense that just about every club on the planet would have him in their team, however, due to the cost he is priced out of the market.
If the transfer of Neymar nearly broke the bank of one of the world's richest clubs in PSG, at £200m. Let's assume that the max they (or any other super-rich club) would be able to spend, due to FFP, is around £250m.
That mean Messi's value is somewhere between £250m and £618m.
Now, I'm not for one minute saying Messi is as good as Leon Clarke, but it's just another example.