Anyone can choose to not trade with anyone else. No one is compelled by law to trade with anyone else. It's just that simple. Complications arise when deniers of service give their reasons for denying service. Just say nothing, or no thank you, even if 'no thank you' is a non sequitur. No one is compelled by law to trade with anyone else, nor do they have to give a reason for not entering into a trade with them. I have declined to work for people for a number of reasons. I do not disclose my reasons. I very politely, and quite simply say no thank you. I've never said that "I don't take drug money" or "I know that you stiffed the last contractor that did work for you." I don't even trade ideas with those people. No trade. No exchange. No thank you.