Large quantity of gil disappeared.

[CKNovel]

Would think it falls under profiteering off other players cheating. That is a thing you know, and this could fall under such a scope when its clearly done with clearly malicious intent. When they should have reported the cheater. So no, they are both in the wrong. You will not change my mind.

There IS a malicious intend.
But that "exploit" is only possible if someone is using a bot.

This bot shouldn't exist and therefore shouldn't be taken in account. The rule always has been "use it at your own risks".
If you remove the bot then there is no exploit, no reason for the GM to ban the one who acquired the gils.

Imagine you're driving. You don't give priority to someone and you crash (and survive unscathed, few).
Turns out the other driver involved was driving triple the speed limit and you couldn't possibly know he was coming at full speed. Is he able to say that it's also your fault for not giving them the priority, even if you actually saw them?