One thing available at nail salons that's not posted on any service menu is a contagious skin disease. With all the hands and feet passing through a salon each day, the odds are solid that some of those appendages have warts on them.
Warts are caused by a contagious virus called human papillomavirus (HPV). There are many different strains of the virus (such as the type that can cause cervical cancer), but only a few different kinds spur the overproduction of skin cells that results in warts.
Warts spread through person-to-person contact when HPV makes contact with a break in the skin. Hands play host to both common warts and palmer warts. The tops of feet may also have common warts, while the bottoms can have plantar warts, which grow inward due to constant pressure between the foot and the ground. All of these are contagious.
Warts can be spread if a salon worker uses the same pumice stone for different clients. Most salons offer new pumice stones, and you can always bring your own to lower the risk of getting warts. You should also frequent salons where employees wear plastic gloves that they change between appointments.