This is a major problem world wide. I am surprised how even large reputable firms seem to think they do you a favour by ringing and emailing for free support. They just do not get it that if they employed someone on staff they would spend orders of magnitude more in wages and have a third of the productivity. I do not know the answer but think as someone has already add that a contract at purchase or sign-up time that clearly spells out what they get and what they pay. I have come to the point where I will no longer take on a client unless there is an agreement and that payment is made by direct debit which means I do not have to chase them for small amounts of money.