I read a thread last year from a colorist who said the clients she lost by being honest always came back or sent referrals, while the ones she rushed ended up costing her way more in fixes and bad reviews. That stuck with me because it flips the whole "bad business" idea on its head, since a wrecked head of hair tells everyone in town what you did. You did the hard right thing, and the money you lost that Saturday is nothing next to the rep you kept.

My cutoff is when the machine is 4+ years old and the idle temps are already creeping past 60C. Had a 2017 HP Omen come in last month, idle sat at 68C, paste was so dried out it flaked off like old paint. Fresh paste knocked 25C off the idle temp and the fan finally stopped sounding like a jet engine. If it's under 3 years old or still running cool, I just blow out the dust and send them on their way.