cant you use escrow..
i think if you will use satoshi box no one gonna buy as there is danger of getting cheated with fake .txt files and scripts.
I sell my script gave a copy of the script to check the person above your post confirmed. I do not wish to cheat and meyu I sell my work.
If you really may need, and can develop a new design for this but write to the PM.
I added a new store to buy -
cryptothrift.com