What should I verify before hiring a roofing contractor?

Four things, in writing. A state licence you can look up. General liability and workers compensation insurance, verified by calling the insurer rather than reading a certificate. A written scope that names the shingle, the underlayment and whether the decking is included if it is found rotten. And the manufacturer warranty, which on most shingles is only valid when a certified installer does the work. A quote that is materially cheaper than the others usually excludes the decking.