Is my estimate final and binding?

An estimate is only an estimate. Vehicles are designed (e.g. bumpers) to cover support systems, brackets, impact absorbers, steel reinforcements, intrusion bars, etc. in a manner that makes it impossible to see all the damage. We need to disassemble the damaged areas to be certain complete repairs are made. With this in mind, it is likely that there could be additional damage to repair, or additional parts ordered. Your insurance company is very aware of this. When they write an estimate they will advise you to take their estimate to a body shop and have the shop call them if additional damage is noticed.