I would have replied "no thanks, I will be leaving you negative feedback, learn how to use ebay idiot."
Seriously, after getting that kind of email I wouldn't even want to fucking deal with him further. He can eat shit. Keep looking man, something will pop up.
Because:
Either:
A: You force him to sell at that price, he gets pissed and breaks your tubes or something (new tubes would be a bastard).
B: He eats shit and actually sells for the price sending you the amp, but leaves you negative feedback just to be a tool.