This is the approach I propose to make this deal happen:
Background on the chip ordering process:
The person who can prove that he/she owns the sending BTC address has the right to tell zefir (=the guy who I ordered the 20 chips from) where he should send the chips.
Also, if you want to have your chips assembled (e.g. burnin's thread:
https://bitcointalk.org/index.php?topic=179769.0) you need to prove that you own the BTC address;
How to prove that you own an address:
To prove that one owns a BTC address one can sign a message using the private key for this address (works in the official BTC client). Other people can verify the resulting message signature and this would prove that you own the private key to this address.
I did this for example in my forum post.
Now, to come to the point:
If I give you the private key to the Bitcoin address, both of us could sign a message to prove that we are the rightful owner of the address. Of course you could trust me that I wouldn't do such a thing.
To overcome this problem I suggest the following approach:
1. You send the 1.72 BTC from an address that you control (=can sign a message with) to the ordering address (1wZKwZ7kEqdsZyDjYuFR7okZYiKV4KhcD)
2. I then send the 1.72 BTC to an address controlled by myself and embed a message into the blockchain stating that <yoursending address> is the new owner of 1wZKwZ7kEqdsZyDjYuFR7okZYiKV4KhcD.
That way, since I don't own your sending address, I can't prove anymore that I am the rightful owner of 1wZKwZ7kEqdsZyDjYuFR7okZYiKV4KhcD
3. I will then send you the private/public keys to 1wZKwZ7kEqdsZyDjYuFR7okZYiKV4KhcD and archive my own copies.
4. We make this transfer public in the bitcointalk.org forum, you should cite my posts so that even if I should delete my account or all my posts the public still has a record of it.
Feedback on how I could improve this is welcome!