Put three bids side by side on identical terms: verification, scope, materials, warranty, price, and gut check — the fair fight the door-knock is designed to prevent.
Get at least two bids — three is better — and compare them on identical terms. A bid that resists this worksheet ("we can’t itemize," "price is only good today") has answered your question. Fill one column per contractor.
Verification
Printable log — columns: Check, Contractor A, Contractor B, Contractor C.
Verification rows (mark ✓/✗ per contractor above)
License verified on state/city site (not just a number on a card)
GL + workers’ comp certificates received from the insurer
Physical local address, verified via business registration
In business locally 3+ years
References from 1+ year-old local jobs — called them
Manufacturer certification verified on manufacturer site