If there isn't cheating why should the seller be penalized.
i don't know the exact skills from him, but i believe you asked this question because the transfer might look weird. And maybe it is, when the transfer estimation is right in this case.
I expect the GM to be experienced enough, to get an good estimate on this transfer, and if they believe it is right they won't do anything. If they think you pay way to much for him, because you get this player normally for 5% of this sum, they will regulate the price to a fair amount for other sellers who don't have the luck to find you as a bidder.
If you don't manage it, maybe the gm think that you only want to give the other team your money, and that why you are paying way to much for him - so better report it yourself in this the gm know you areN#t looking for transfering money betwenn teams. What do you think "real" cheaters say, if they get caught? I think they will say, things like this
If someone wants to pay that much so be it
and it isn't easy to see if it the truth, or if evidence is right and this was a cheating transfer.