Nope I think your right, I think its fair enough to try a cheeky bid as you never know and everyone like to think they are getting a bargain no matter how cheap things are, but when told its a firm price the OP should respect your decision and either stump up or bow out.
I have tried a few cheeky offers myself in my time but have always accepted the OP wishes, Rude is just Rude.
Good luck with the sale