I think the question of the OP is how are the trades matched?
E.G.
If there is already a sell order at 10 each and you want to place a buy order at 12 each, how do the exchanges decide what is traded? Are they matched at 10 each, which is what the seller would accept, minimum, giving the buyer, effectively a discount.
OR
Is this settled at 12 each, which is what the buyer was willing to pay but giving the seller a better deal.
That was exactly what i asked