A referral is an introduction. It is not a background check you can skip.
The license
The Contractors State License Board publishes license status at cslb.ca.gov. Look up the business name on the quote, not the name on the truck if they differ. Read whether the license is active and what classification it carries. Pane Pro SD does not do this lookup for you, and we do not publish a list of approved companies.
Insurance
Ask for a current certificate before work starts. We do not keep those certificates and we do not promise coverage.
The quote
A useful quote names the openings, the product, what happens to the old frame, who flashes, and who patches. A single number with none of that is not something you can compare.
If the scope includes a permit, name who pulls it. Start with what to ask about a permit.