It's happened to almost every car owner. You're driving down the road minding your own business when you get involved in a collision. Or somebody isn't paying attention in a parking lot and you wind up trading paint with another car. Or you come out to your vehicle to discover that some moron has dented or scratched your fender and then ran off.
Almost everyone seems to experience the same immediate response.

"GaaaAAAHHHHH!"
Eventually, they contact their auto insurance company and file a claim. After all, that's what car insurance is for, right? To pay for those unexpected repairs (after you meet your deductible, of course).
But how do insurance companies figure out how much to pay for? What's their estimating process like?

"Tell me the price of a front quarterpanel on an '05 Mustang!"
Each auto insurance firm arrives at their estimates a bit differently, but the basic process is pretty much the same. Insurers document what needs to be fixed or replaced, come up with a figure for how much it will cost, and work with a repair shop to complete those repairs.
Many companies employ appraisers who will visually inspect your vehicle for damage and formulate a report describing what they found. In some cases, photos taken by the vehicle owner can be substituted for an appraiser's report.
Most insurers use what is known as a Mitchell Manual as a reference for tabulating parts and labor costs for a given repair job. This piece of software (which used to be packaged as a huge catalog in the pre-computer days - hence the name) lists the approximate price for every part, feature, or accessory on every type of vehicle, along with the labor costs associated with its installation. The computer program uses this data to calculate the total cost of a repair, then subtracts the policy deductible to arrive at a monetary amount to be provided to the car owner.
Some auto insurers ask that the vehicle owner get one (or two or three) repair estimates from local repair shops. These estimates are then factored in to the final coverage amount given to the policyholder. Different insurers place different levels of emphasis on these customer-provided estimates.
Auto insurance companies have relationships with numerous repair shops around the country, and they work with these shops to negotiate repair prices for their policyholders' vehicles. However, you can always ask that the work be completed at a repair shop of your choice. In these cases, insurance firms either consult with the chosen shop directly or simply give you a fixed dollar amount to be used for your vehicle repairs.
Your insurance agent can probably tell you more about the nuts and bolts of your company's repair estimation process. But you can feel secure in knowing that your auto insurance provider will do whatever it can to keep you happy. They know that the auto insurance market is competitive - and that dissatisfied customers have plenty of choices if they want to switch insurers.

And now, the mandatory shameless plug.
Image credits: growingguides.com, villagetattler.com, online.safeauto.com.