I think I know a bit about how gil sellers work overall. I hope it will help some players understand the situation of combating gil-sellers and hopefully help SE get rit of them.
Ok, gil sellers come in 2 forms:
The 1st one being an intermediate dealer (like ebay) who will buy gil/equipments of other players who are perfectly legit but just want to earn some extra cash OR those who are quiting (and sell their accounts). Their primary dealing was with accounts and gil. So, at most they will have a few mules to store the 'bought' gil and to send them to buyers. Their business was flickering at best since the 'supply' of accounts and gil from servers are uneven; more than often they have to adjust their price rapidly. They don't have any bots or playing accounts so they were somewhat tolerable until the 2nd type of gil sellers came. Or rather you can say that the 1st form get beaten and evolved into the 2nd form.
The 2nd type is more like a farm. One person (or a group) buy a place with several computers - kinda like an Internet cafe. Then he employs people who are paid-to-play. They are pretty much from a low income area and the idea of pay-to-play is appealing. They play in shifts, just like people going to work in a factory. Playing is their job (making gil or powerleveling). Well, this form generates those code names and jerks and bot-alike players. I'm not sure if these guys actually use bots or not but I'm quite certain they are the type that appears 24/7 on all servers. The gil the 'farmers' earned will be send to a certain storage gil-mule.
A long time ago, their methods were inefficient and very rough. Overtime, people with a certain knowledge of the game and english started to join (because it's a growing business). The farmers upgraded from endless farmings to crafting, BCNM, parties, NM, HNM even areas like dynamis/limbus/sky..etc are slowly acquired. Pretty much anything party/LS/HNMLS do are copied. They are growing more and more sophisticated and become extremely efficient in getting gil. Perhaps even more than an average LS/HNMLS since they have lots of man-power at their disposal and no LS-drama and excellent communications since they are just a arm away from each other. With the addition of rare/ex gears to prevents trading, they equip themselves with just those rare/ex they found along when they do missions/bcnm/hnm... etc to improve their efficiency.
Methods that have been used to eliminate RMT, each of these method have it pros and cons:
Banning/Block IPs: This was used a long time ago to effectively filter out the unwanted zones. This is extremely good when the company only sell the game to a certain area with a specific game ID. If you get a game ID of US coming from an IP in Asia then it can smell trouble (like WOW). An effective KILL 'EM ALL method. Of course this only works when "imported" games are not supported/allowed or are very localized (WoW, Ragnarok Online). Slowly it get countered by the use of proxy servers. Many gil sellers bought their own proxy server to counter banning ips.
Limiting game features: This is what SE did for the delivery box, claiming, fishing...etc. In a way it effectively reduced the means and methods for botting, cheating and explotations. The delivery box slows down the 'trades' of gil sellers, forcing them to use the San D'Oria area (I think they use Jeuno to trade too) to trade. This means it's easier to observe the trade and ban them both. Claiming and fishing are anti-bot functions so there's nothing to be said much.
The major drawback of this method is reduced-functions of the game. Let's face it, if you limit certain functions of the game then you're taking out some of the fun of it. HNMLS leaders will now have big trouble distributing gil/gear. Before they can simply send the 'paychecks', now they have to meet each LS member personally to trade (not a fun thing to do if you have like 40+ people). Fishermen can no longer fish for extended period of time even if they want to.
Banning accounts: This is the most common methods and have proven to be the most effective method in getting the 'right' target. Primarily it was used to get rit of bots, bad players and evil demons. The gil sellers suffer a lot from this method since once an account is banned they not only lose the resource in that account but also the money spent. Legit players getting banned often wrote letters and complain until they have their account returned. Gil sellers didn't do it until they realized it is possible to do so.
This method has the greatest drawback is that the company needs to separate the normal players from the bots, bad and demons. More than often you will get some players doing crazy stuff and you can't just simply ban them. A particular fisherman happens to enjoy fishing a bit too much shouldn't be banned but he can be mistaken for a bot. A poor drg who's determined to get his lovely SH and went out farming at ONE spot for months can be mistaken for a gil seller. Obviously when you see a drg farming exclusively in the tower you're bound to believe that he's a gil seller but if you ask around you will find some people actually farmed there for a very very long time to earn gil. A particular player having a mule which is used to craft and sell shihei exclusively can also be mistaken for a crafting bot. Well, once you realized there are people making 500 stacks of insect balls to fund their main job then you will know not all crafters are bots (yeah, I crafted 1000 stacks of insect balls when I was low level to fund my ranger/woodworking).
Massive account banning: This method was uncommon until recently. This is because gil sellers were very very isolated. They did most of their gil-earning alone (farming, crafting.. etc). Until the emergent of the 2nd form of gil sellers, they started to work together. Obviously, since most MMO are aimed towards working together on BIG-BAD-BOSSES and earn big money/gear; They often make party/alliance work rewards to be much better than solo work. The 2nd type of gil sellers are doing just that. They are working together, taking advantage of the features/rewards for 'working together' to become more and more efficient at their trades. Of course, when you have a bunch of rats running around together you will want to throw a Firaga III. Game companies did just that. KABOOM! One massive attack to kill them all since they are all together anyway. There is no miss-firing here since normal players will play 'normally' in LSes that act 'normally'. Sometimes you get a stray shot of some people getting too close to gil sellers. Gil buyers and people who pay to have the gil sellers get them a certain item (notice the Black Belt items are now possible to be bought with real money). Well, they are baddies anyway so they deserve to suffer.
This is the best way to drive them out of business. If you ban multiple accounts then the gil sellers will not have enough money to recoup their losses. More than often they will suffer a large debt. Even if the ban is temporary, the lost of time if waiting for the return of the banned accounts is enough to force them to go out of business. Once they are out of business, returning accts to them wouldn't do them any good since they are out-of-business anyway (maybe for reselling to another gil seller?). Normal players do not suffer much more such activity since they will be more persistent and are willing to wait for their acct to be returned.
The greatest drawback of this method is like police work. Unless it's extremely obvious to spot (like having similar names) you will need to have a pretty good idea of how these gil sellers are working together. The reason they have a set of common names is for cataloging, naming and recognizing. If they use a generator or a list of names then they will not be easily spotted. To simply put, they are EXACTLY like a normal players. Kill several targets to earn better gear/money. Collecting rare/ex items and distribute to members. Pool all the loot and sell/craft on AH to make the best gil out of it. The only difference is how they use the gil. Normal LS will have a 'paycheck' for its member, some of the gil/items will be kept by the leader for LS purposes. The gil seller will get 'paychecks' in cash form and all the gil/loot will be send to a particular mule to wait and sell to other players. This means finding evidences for their crimes will actually require infiltration (police work!) and bugs (read chat logs). Now if the gil sellers are... communicating using voices then it would be near impossible to know which is which.