The sources of variability in service delivery from the options provided are:
- differences in the quality of the hair products (shampoo, conditioner) used at the salon
- differences between service provided by the same stylist at various times of the day, week, or month
- differences between the service provided by two stylists working in the same salon
- differences in appointment scheduling at two different branches of the same salon
The option regarding "differences in the prices charged for hair care products that can be purchased at the salon" does not directly contribute to variability in service delivery, as it pertains more to pricing rather than the delivery experience itself.