Folks can always buy gear but they cant buy experience. They can rent it by hiring a guide.
Crampons arent required above treeline as long as the conditions do not require them, the down side to not bringing them is having to turn around. A big issue is most people can climb up steep stuff far better then descending it. I have run into folks that have gotten into a fair share of problems where they managed to make it up a slope and had a real tough time heading down it. Ammonoosuc Ravine and Lions Head Winter route both usually need crampons. Falling Waters, The Old Bridal Path section above treeline especially on the NW side can definitely be a crampons not optional section and Liberty all on occasion need crampons.