For a single isolated transaction that may well be fine; when (for whatever reason) there is only one possible vendor - the last parcel of land blocking a scheme for example - that vendor is using the law (of private propoerty in that case) to exploit the other party quite as much if they choose to hold out for an unreasonable sum. The whole purpose of this system is to determine a fair means for the transaction as a whole to proceed without either party being able to unreasonably exploit the other.