Surrogate mom vs parents?

Andrea
This is a question that has been curious to me for a long time. I mean no offense to anyone asking this. But I've seen cases where a couple will pay a surrogate mom to conceive their child, everything from cost of living to medical bills, but when times comes the surrogate mom sometimes has other thoughts and decides to keep the child. My question is, in your opinion, do you think the surrogate mom should have any rights over the child when the parents have paid for everything and the forms are cleared through?