I understand completely - I once had a girl ask me for a 50% discount and to customize the item for her. Uh, nooooooooooo. Unfotunately, a polite "no" didn't work because she sent me 20 more messages asking me to donate it to her, comments on what she didn't like in my store, which pictures needed fixing, etc. At a certain point, you just have to say, "If you don't like it, don't buy it."
(There was no transaction involved.)