My first thought was to be nice and forget about it. But he did have 7 days to think about his auction, and pull it if he was unhappy with it. A $75 opening bid with no reserve is a chance he took if he thought it was worth more than that. I have sold things at a loss on ebay before, but I knew I took that chance when I listed it, and did not complain when it sold.
I am a pretty easy going guy, and I don't really want him to be upset with me. But on the other hand,I don't think it right for him to be able to back out of a deal like this.