The real truth is that insurers DO NOT guarantee the work of their vendors. They do however require their vendors to guarantee their work. Firms that offer a guarantee through the insurers that they are a part of, have absolutely NO competitive advantage to those not on vendor programs. Stand up for YOUR rights and have your own Guarantee as has already been mentioned.
There has been a time or two where an insured will be told this nonsense by a desk adjuster usually, and I simply add a year or two more than what their providers offer.