I've seen this pretty regularly with artists taking commissioners. If you actually want people to commission you, RESPOND TO THEIR QUESTIONS. Unless the said individual is flat out disrespectful. If a person is ready and WILLING to buy more than one commission and not sure the total, DON'T HESITATE TO QUOTE THEM A PRICE (and be clear . If you find their character to be "too hard, uncool" rather than IGNORE their references, politely tell them what you "won't do" or that they should change it.
Also a REALLY BIG peeve, IF YOU CANNOT FINISH A PERSON'S commission YOU SHOULD APOLOGIZE AND REFUND THEIR MONEY. I have seen WAY too many people TAKE their commissioner's money and ignore them.