The Gmail Address on Your Work Truck Is Costing You Jobs
A Gmail address loses the tiebreak when two bids are close, and anyone can register a lookalike for free. Mail on your own domain costs $7 a month, carries authentication a Gmail account cannot offer, and moves over in an afternoon.
If your estimates still go out from a Gmail address, I can set up mail on your own domain as part of a site build: mailbox, authentication records, form and invoicing checks, and the old address forwarded so nothing gets lost.