I sell my transerable items no-mod, if people want a moderation they can always im me and ask me to make it (no extra charge) or I send them a mod version.
I started to sell my trans things no-mod after a couple of buyers that claimed to have messed up and asked for a new item and that happened a few times in a short period. I got a strange feeling about that, since the last person I asked to send the messed up version back (after all it was trans) and they just emptied their trash.
When I send a trans/mod version on demand, I do tell them that I am not handing an other when its messed up.
So in answer to your question, I do it to prevent discussions.
I only custom build and sell through marketplace, so my customers are told or see that they can always IM me with questions or changes.