Why is the certificate not signed by your PGP key?
That would be because, like most people, I don't have one!
Anyway, even if I did make one, it would be new/untrusted, and it would just confuse 99.9% of people on Ebay who saw the auction.
I'm going offline for the evening - you guys all bid so I can be happy tomorrow morning, k?
If the auction ended right now, some lucky person would get their bitcoins for just over $1 each

Hopefully I'll have some snipers when it ends.