Not on price, I know, but they may negotiate on whether we buy direct from them or whether they make the player buy himself out. To them it makes no difference on the fee they receive.
But to the buying club it means either pay the fee to Bilbao or pay the fee plus the tax the player will have to pay , as if we pay the player to buy himself out he pays tax as it's income. So staying on the right side of Bilboa is beneficial.
For example if we wanted to force the release in January Bilboa would force us to pay the player to buy himself out and it would cost us £51 m plus tax. If we negotiate and agree to wait until summer they might just agree to sell him direct fot £51 m.