First of all, good luck with the sale, hopefully both you and the buyer will be happy. second of all, your attitude stinks - you hit the nail on the head in your original post - it's not ebay, buyers have no protection so have every right to offer their twopenny worth, if you didn't want to hear it then perhaps selling it on CL or ebay would've been your better option. There's no call for insulting other people just because they have different opinions to you on what a 'bargain' your flash is!
It's not like its a gold-plated leica that was once used by Robert Capa - then you might be able to dictate the whole silent auction thing - it's a flash, simple as that, there are thousands just like it for sale out there, some at prices higher than yours, but a great many at less. Losing a bit of the attitude may well get you a sale, which is after all what you want i'm assuming?