Man, my siding guy once framed a window around a hose bib and I didn't notice for two weeks.

Prep issues on used liners are way more common than people admit. Ran into the same thing on a stove pipe I picked up cheap, and scuffing it with 60 grit plus a good wipe down with denatured alcohol made the difference between the coating flaking off and actually bonding. Two test burns holding is a solid sign you got it right.

Man I felt this in my soul because I did the exact same thing last spring, got quoted $11k for 22 squares and proudly told my wife I'd "negotiated" it down to $10,200. Turns out I just negotiated myself into getting robbed. My barber's brother does roofs in Aurora and laughed at me for a solid minute when I told him. Once you know the fair range is low 6s to low 7s for that size, that $9k number stops looking like a quote and starts looking like a dare. I'd call the guy and just ask straight up if he can get closer to 7, no hard feelings either way. If he gets weird about it, you already know the answer.