Insurance companies, as least the larger reputable ones, don't simply allow an adjuster to make up a random number to try to beat the insured out of the value of his car or truck. The adjuster goes to whatever price guide the company uses, plugs in the odometer reading, and his experienced opinion of condition before the damage, and a number pops out. There is not much room normally for negotiation and the amount the insured paid for the car or truck and the amount, if any, he or she owes means nothing to the appraiser. They don't assign added value for DTT transmissions, fancy wheels and tires, or other expensive additions or improvements. The actual value is often a harsh reality to the insured.
IIRC, the adjuster will contact regional or local salvage yards for bids on the wreck if a total. Whatever the salvage yard bids is the price the insurance company will take for the insured to buy it back.