There are many discussions of when the fingernails can and cannot be cut according to halacha and minhag. It is very hard to ascertain anything coherent from this information, other than that Friday is the best day to cut them, and that many other days may be prohibited.
Is it acceptable, however, to have someone else, such as a manicurist, cut your fingernails for you on the "wrong" day? Does it matter if the person is Jewish or not? Please bring a source.