That whole thing @hollypalmer mentioned about smelling burning hair... it's wild how many services just default to the highest setting. Like with vacuums or car washes, they assume more power is always better, even when it's damaging the thing you're trying to fix. It takes someone speaking up, like your Denver client, to make a change.
I actually read a study a while back about how different hair types respond to heat. Fine hair, especially, can be really sensitive to high temperatures. I remember it saying that a lot of stylists just crank it up because that's how they learned, but it's not always the best approach. I bet your Denver client had a finer hair texture, and that lower setting probably saved her from some real damage. Your mileage may vary of course, but I've seen plenty of folks online say their scalp is way more comfortable since their stylist backed off the heat.