It depends on whether we're talking about estimates or negotiated rates.

In the latter (also called "preferred rates" for auto insurance) there's a blanket agreement that all work of a certain type is to be billed at a fixed, negotiated rate.

That is VERY different from a binding estimate, which typically means a one-off estimate for a specific job where the estimator takes the risk and promises to complete the work at the rate, even if it's much more complicated than they bargained for.

There's also whether they will pay at all for some things. They have some discretion to claim some damage was existing, or unrelated to the claim, caused by the repair shop, not normally covered, etc. Or where they won't pay for OEM parts if some substitute is available. There's lots of ways they can shuffle around.