does casascius keep a copy of each private key that he produces? I've always wondered how trustworthy they are
That's what he says in his Q&A:
Q. Do you keep a copy of the private key? Who has had access to the private keys?
A. I did not keep the private keys, and I am the only person who has ever had control over the private keys. I have either inserted the private keys into the coins myself, or have directly supervised others doing the same. On the series 1 coins, the hologram manufacturer pre-printed the addresses onto the hologram labels, but they were only given the 8 characters you see, not the private keys themselves.
Q. It's impossible to prove you didn't keep the private keys, and with all the Bitcoin scams lately, why should I believe you?
A. I have given out my real-world identity and have digitally signed a list of the Bitcoin addresses used in this project. I have made it so that it if I were to perpetrate a scam, it would be possible to prove it and to hold me legally accountable - something no scammer wants to do. You should demand the same from anyone handling your cryptocurrency.