My Tuesday from hell turned into a $600 lesson about dryer vents

So last Tuesday I had three dryer calls back to back and the first two were the same thing, clogged vent lines. First house in Garland, the guy had a 14 foot run with two 90s and I pulled out a wad of lint the size of a cat. Second one in Mesquite was worse, the flex hose was crushed behind the unit and the vent hood flap was glued shut with lint. I quoted the usual cleaning and he asked why his old guy always said just replace the whole vent. That got me thinking about how many of us just swap parts instead of looking at the run. Third call was a Kenmore that would not heat at all, turned out the thermal fuse blew because the vent was packed solid. So I cleaned the vent, swapped the fuse, and it fired right up. I made $600 that day but the real win was the guy in Garland calling me two days later to say his clothes dry in one cycle now. How do you all price vent cleaning jobs, flat rate or by the linear foot?