Will a bill of sale be enough documentation to prove ownership of my vehicle when my car was declared a total loss?

Most states give you a few days to register a car in your name. In addition, insurance companies usually allow a few days if you buy a replacement or additional car. If the other person’s insurance is going to pay to repair/replace your car, they should accept the bill of sale as proof of ownership. That, coupled with the title in your possession, should resolve any question of ownership. However, if the insurance company is hesitating, you should see if the seller would provide a statement to the insurance company confirming they had sold you the car. If you continue to have problems with the other insurance company you should contact your agent or company to see if you can file a claim under your insurance. Presuming you had collision insurance, you would be paid, less your deductible. Then your insurance could go after the other insurance company for reimbursement. If they are successful you would get your deductible refunded.