How to earn Gil at Endgame

[Amyas]

See those tin,silver, gold pieces you got at the end of quests? Yeah those, they are thrown at you if you do dungeons. Go farm dungeons.

Far more likely to get tin and bronze, which almost aren't even worth the inventory space. If you have like 50 tin pieces they'll only sell for what, 500? 50 silver pieces only give you like 8k or something like that iirc, that would take lots of farming...