Itemise the prep
It is the whole difference between quotes.
One of them includes the hours nobody sees, and the other one does not.
Paint is the cheapest part of a paint job. What separates a finish that lasts eight years from one that looks poor in eighteen months is the filling, sanding, caulking and priming that happens before any colour goes on — and it is exactly what a low estimate quietly leaves out.
So the useful question to put to any quote is what preparation is included. An itemised estimate lets two bids be compared on the same basis, and it is also the document you need if the finish disappoints later.
The other discipline is refusing work. Painting over active moisture, failed caulking or rot produces a coating that fails within a season regardless of product, and the owner reasonably blames the paint. Naming the cause and declining to coat over it costs a job and saves a customer.
It is the whole difference between quotes.
The paint will fail and get the blame.
Contained areas, and the pamphlet first.
A free written estimate with the preparation spelled out.