I know this is between you and conitec, but it's so simple I'm going to butt in:
a) Password.txt: this is the password file that allows you to download the files. Seller gives this to buyer.
b) key.exe (or key.zip): this is the key that will unlock the trial version and upgrade it to the current version. Seller gives this to buyer.
c) Registration: This is an internal Conitec database that states that you have transferred your license to another user. Conitec handles this at sellers and buyers email request.
What you are probably wanting to do is have the "registered to: sorceror" tag on the development startup screen have your new buyers name. If I'm correct, to do this:
1) The registration process (point "c" above) must be completed.
2) The new owner has the key and password files.
3) The NEW OWNER requests that Conitec make a new key to reflect his name
OR
3) It's conitec's policy that they don't change the name in the dev version (since it's pointless anyways) and they just know internally who owns what.
So in conclusion I think all you need to do is make sure your buyer has the key and password file and then have the buyer request whatever it is they want.
Hope this helps and if not I'm sure JCL will be here to clear things up!
