As far as feedback is concerned, that is a tough one. The way I see it (apart from charging you $5 for a $0.37 stamp) you have to decide if you believe what he told you. If he is telling the truth, he is out both the tickets and the money, so a negative feedback for overchaging for shipping might be overkill. If you think he is lying and just shipped them late or something, well then he deserves a negative feedback. It all depends on if you believe he did everything he was supposed to do in a timely manner.