Isaol-the-wolf
Some people seem like they have had a total of at least 100k gaia cash.
It took a long long long time to build up the wealth I have now. I've also never once ever sold off any items given to me or sold cheaply to me.
I get most of my money from 3 sources.
Event items - Hold on to them for a long time, then sell them off once and a while. Items you earn tend to have better end prices.
Daily Chance and Aquarium - It's often overlooked, but if you go and get stuff -every day-, then you'll slowly build up some nice wealth. Every month or so, just go in to organize inventory and sell off all the free crap you get and you can get a few 1,000g...probably on average 2,000. Not too bad really, considering it's free.
Playing the Market - I don't really do this as much as I should, but I can make some good money now and then. If I just want an evolving item for purely just the item and poses and stuff, then I go for the cheapest one available and don't go for the first one released. I may do this with the Infernal Spirit. I sold it off when it was doing pretty well and then I bought another evolving item. I kinda want it back though, and now it's worth more than what I sold it for. xd