Marisa, I don't think that is being rude at all. It sounds like you have been very accomodating. I think that if a person is seriously interested in a certain type of snake and finds one for a fair price and free delivery, they would take it. To me, these people sound like time wasters that aren't so much interested in corns, but getting a cheap snake period. If you do end up selling to them for a reduced price this time, they will want the same if they buy from you in the future, and you will probably have to go through the same dickering again. I realize breeders have to consider their reputation and it's competitive especially if it is your sole income, but I think serious buyers would be happy with what you are offering.
Life is uncertain, eat dessert first