I'm going to ramble.
Yes, the main thing that caused gil selling in FFXI was vendoring goods. Why? Because it created more money that wasn't currently in the system. There are two ways actually and this is one of them. They quintuple box or whatever entire groups and sell tons of things to NPCs to make money, then sell it online. Since it is literally created by them then it is more money in the economy that wasn't there before.
They did it through fish bots/caps for a long time in FFXI not through mobs, but in EQ2 it would be through mobs. In EQ2, however, if they find a "sweet spot" that's easy and gives lots of adepts or whatever that sell to NPC merchants, then they can actually shut off their xp and put in an 8 hour day of this making insane amounts of money. This is a very bad thing.
Creating new money is not good for the economy. It leads to inflation because with more money in the economy people can spend more on things. Now yes, if the money were evenly distributed then it wouldn't matter. The problem lies in the fact that it is not evenly distributed. Just like real life, the most money is actually in the hands of a very few. It's a x^2 curve; I've seen the graphs of SWG's currency distribution. So the have nots are very very out of luck, 50% of the population is this group.
The less money in the economy, the smaller the difference between the rich, the middle class, and the poor. Which means it will be easier (although still painful money-wise) for the poor to afford things. When there's a lot of money in the system, it starts to break down because the rich can drop what is a fortune to most people on something and not feel a thing. That's when you'll see coral going for 10 plat just because somebody will pay that for it, simply because they want it NOW and 10 plat won't hurt them much.
This is waaay down the road, though. I'm thinking in a year's time. This is why we have things like the broker to take out 19% of each purchase (it isn't 20%, not sure if that's a bug). That's what money-sinks are for, to try to even out all this money coming in. In the perfect system, money going out would equal money coming in. The more NPCs buy for, the harder it is to funnel all that money out of the economy.
The easier it is to get money, the higher prices will be. If I could go out and make 1 gold per hour easily, then that coral would be worth 10x as much as it is now, simply because it would be easy to find a buyer who would pay that much. Also, the easier it is for casual gamers to get money selling to NPC merchants, the easier it is for power gamers to run this into the ground, furthering the gap there. The easiest way to solve this is to make one time quests the best way to get money so they can't be run over and over again. They've done a fair job with this.
This is the reason they've been nerfing crafters selling goods to npcs. Because they don't want lots of new money coming into the system. And since most players are adventurers, the retaliaion will be slight if any for this.
But in short... um... new money bad. Recycled money good.