It may happen, but this is something that you should be very careful about. Clients may want more than just a professional relationship, which can be very tricky. If you reject them, you may lose them for good as your clients. But if you keep seeing them, even if you made it pretty clear that there will never be something more than a professional relationship, you may still encourage them to hope for more. So you have to take the detours and be very diplomatic. Things like this do happen very often.