That would not tell you anything about how much someone values a product. Everyone will happily pay 0 for something they value at 10. It's a fantastic deal for them. Too discover the true value you have to raise the price until they refuse to pay it. Which is what a market is intended to do.
What? You don't think the two measures would converge? In either case, the one with more market power would use that to improve their side of the bargain? Who'd've thunk...