There are no rules requiring multiple proposals or that you go with the lowest bidder. It is not required that homeowners get 3 quotes for insurance inspections or work, despite popular opinion.
Often, the insurance companies have captive or dedicated insurance restoration contractors like Servpro, Puroclean, or Service Master who will perform most or all of the work for an insurance claim without outside bids or competition, further illustrating this point.
The insured or property owner is free to choose who they would like to perform the restoration work. The insurance companies use a standardized bidding platform called Xactimate to create preliminary estimates and guidelines for the amount of money that should be paid for claims.