With her children grown, Trisha Eck thought it would be fun to go from being a stay-at-home mom to a small entrepreneur—so she rented a room at a medical spa, where she started her own business, Tooth Fairies Teeth Whitening. She purchased equipment and supplies from a vendor she met at a trade show, including non-prescription strength teeth whitening gels. Customers could purchase her products as a take home kit or apply them to their own teeth while visiting the spa. Since she’s not a dentist, Eck says she never performed the treatments on customers but was there to offer...