He combines the keys, he already has the public address which is either funded or not (his choice), I do up some final work on the item to have the public key and voila, I shop it out and they have a completely secure address.
This sounds like a little more effort on my part and the client's part but I think if anyone is going to 'trust' me, that's going to be the best way (mainly because then you don't have to trust me).
--snip
Of course if they don't want it funded and never really care about funding it then this is irrelevant, they pay their base price to an escrow or myself and it's shipped out.
First of all I have a lot of respect for that you come out and not just assuming that everyone should trust you, "just" because you are making a coin.
I am sometimes surprised about how people are willing to trust new coin producer with their bitcoins, I am not talking about payment but the security of the private key.
When you confront a coin maker about the security, they always say something along the line: all private keys are destroyed, but there are never any kind of clear manifest about the procedure.
I personally think it is reckless to trust a random person with a private key containing anything more than a few bitcents - especially taking the coingraphic indecent into consideration.
The thing that makes a physical crypto coin unique is that it has a private key and it was funded at some point, which is documented in the blockchain.
From this point of view does it not make any difference if it is funded with 1 BTC or 0.01 BTC, however funding the coin with 0.01 BTC reduce the risk significantly for both buyer and producer.
The idea about 2FA or the buyers creates part of the private key takes the risk away from the producer, but it kills the 2nd market for the coin, instead of solely trusting the producer, then will you have to trust the 1st buyer as well, if the passphrase or partly private key is flawed then can the funds never be redeemed by any subsequent buyer.
TL;DR: I like small denominations best (0.01 - 0.05), private key created by producer with a clear manifest of how private keys are handled and destroyed, for the reasons stated above.
These are some very wise words ^
Be cautious when purchasing physical coins and do your research ahead of time.