Coin Exploit

Bad idea for many reasons:

1. Patching the sell back price would not fix the hack. It would only make it so that meso sellers would be slowed down from mass creation of mesos.
2. It would require a complete repatch of the WZ files.
3. It would screw legitimate players

The best way to fix the hack is to include what's taken from your inventory as part of a server-sided script and not part of a packet that can be edited client-side.

Easiest way to go would be an EXE patch which requires no version up.

But the legitimate players aren't NPCing their maple weapons, they're selling them in the free market. Nobody with half a brain would be NPCing maple gear.