Look at low lvl gear and normal items, there isn't a variance in price from nation to nation to jeuno.
I'm not assuming people use RMT, the fact there are tons of RMT on our server. Please believe at 75, people are too stupid to make gil. They depend on god/hnm drops for gil, just sit in an LS and hear people bitch about when they are getting paid.
You got a lot of how the gil comes in, stuff I've already gone over. But you aren't remembering who was running the bots, and you don't seem to get who was in davoi, beadeaux, and Castle O so long. Do you know? Killing beastmen over and over again, getting drops, some that are worthless and npc'd, some they could sell and get nice chunks of old gil for. Regular players don't do this. I've shown up to camp an NM every once and a while, never a legit player, always an RMT.
Rusty caps were a big exploit, and there were some legit players there. But you can ask the legit players who were NPCn stuff, and one has posted here before there weren't as many legit players there as you think. I remember a couple years MPKn new gil seller fish bots in Buburimbu. They were getting them through their levels to become efficient bots. They would have 5-6 new bots every week out there leveling up. The patch was put in place for fish bots in general, majority of them unseen to you.
No matter how greedy a player is, if there isn't enough people with gil to buy it at the price you want, you aren't going to sell it.