May a jewish woman do electrolysis on a male, not knowing if he is jewish or not? One concern is if he is jewish there are places which would not be allowed for him to do electrolysis and thereby be problematic for her to do it for him. Also, being that this is a an medical procedure, only cosmetic, is there more of a concern of a male touching a female, and via-versa?
It is best to avoid doing electrolysis on a man at all even if he is a gentile because of the touching etc. however if you can’t get out of it, it is permitted. This is even if the person is really a Jew.
Although it is surely preferred to avoid such situations because of the contact between you and the customer, however it isn’t really chiba, and she is busy doing her work. Regarding lo tilbash, there are two questions here, is the person a Jew or a gentile and therefore lo tilbash will not apply and it isn’t lifnei iver. Secondly, even if the person is Jewish, it is questionable if we say that since many gentiles do it, that lo tilbash will not apply. Since it is a sfek sfaika that we cannot verify, is the second safek is not verifiable, we don’t have to find out the first safek.