Three years of insisting on fixed bids, finally switched the other way

I ran a small paint crew around Columbus, and I swore by fixed quotes. Every job, every wall, I gave one number and ate any surprise. Three weeks ago a homeowner showed me dry rot behind a baseboard that turned a 2 day job into 5 days. I lost close to $700 on that one. My foreman kept saying we should bill time and materials, but I figured clients would run us around. Then last Tuesday a buddy in Dayton showed me his invoice where the client added a whole garage ceiling after the first coat dried. He billed every extra hour, no fighting, no fudge. That plus a spreadsheet of my last 12 jobs showing I underbid 8 of them did it. I switched to T&M with a written cap for scope changes. Has anyone else made that flip and found the customers trust you more or less?