How do hair stylists at Fantastic Sam's or Supercuts get paid: per hour or per haircut?

My mother is a hair-stylist and she gets paid per haircut.How do hair stylists at Fantastic Sam's or Supercuts get paid: per hour or per haircut?
I heard it's per hour and any per-haircut pay depends on the tip. If it was a per haircut basis, ALL hair places would take walk ins and the stylists would cut hair as fast as possible, which is not the case.