This question could apply to any part of the United States, but particularly to California, which is unusually consumer friendly.
Suppose I am involved in minor car accident (basically a fender bender). It's small enough that some drivers would let it go, but under California law, at least, the other person has the right to insist on even minor repairs. So the person quotes me a price. I dispute it by saying "I can get this done for $200 less. Can you provide a receipt.
The other person can't provide a receipt. Do I have to pay the other person's quoted price? Do I have to the "$200 less" if I can document it?