If your car has been declared a total loss then you are going to have to negotiate the fair market value for your vehicle. Most insurance companies rely on valuation services that tend to the low side. You should have your vehicle valued by one of the free sites like Edmunds.com to see if the insurance company is offering a fair price for your vehicle. Keeping the car is your option but the insurance company may want to deduct the salvage value of your vehicle from the offer.
This, unfortunately, is a very common problem. One way to gain a little leverage with the adverse insurance company is if the facts of the collision contain some type of aggravating factor, such as the person who hit you was drunk or was driving at reckless speed. In that event, you can threaten the insurance company with "punitive damages" should the case proceed to trial. Absent such factors, if the cost of repairs if higher than the replacement value of your car (i.e., your car is "totaled,") the best thing you can do may be to support your claimed replacement value of your car by providing the insurance company with evidence of comparable cars for sale in the area (e.g., newspaper ads, internet listings, etc.).
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