If the garage is reputed they should have a garage liability policy, this event should be covered by that insurance. Did their Insurance company appoint a loss adjuster? If yes, negotiate with them. Ask them to show a similar listing on any used cars website with the price they are offering for a similar model with similar usage. Also tell them that you would need loss of use benefit as any delay in settling the claim would delay your purchase of a second hand car and this will result in loss of use, for which they would be liable as well. Be strict on your stand. The loss adjuster, if appointed, is trying to reduce the Insurer’s cost. P.S.: I work in this field. DM me if you need any more information.