I think this is a novel idea.
I do think SE could help themselves out by undoing at least of the changes made in a past update - the delivery box gil-sending limitation. I honestly don't think it had as major of an impact on players as people would like to claim. If anything, I think it just made it more of a pain in the *** to do simple gil-sends, as I don't really see there being reason for a vast number of > 1 mil sends between legitimate players. Occasional large gil sends to LS banks, etc, and even between high level crafters and their mules would/should never reach the frequency you would expect from gilbuying/selling. Besides that, nothing stops one intermediary bank or mule from recieving lots of 999,999 sends, which is really where the problem arises - the gil pooling - nor does it stop a gilseller from being able to (for example) send you 1 m from each of 8 different accounts. Regardless, the money should be absurdly easy to trace.
Going after websites is good, although it won't get those people who are hiding in the nooks and crannies. This actually quite surprises me, as no MMORPG company to date has been able to shut down a single one of those websites - I've seen more action come out of the Diku team than any large for-profit coorporation. (Diku is a text-based online RPG called a MUD - it's released under GNU, and license terms prohibit profiting from the code...)
And, I would like to agree with all of the previous posters who listed public shaming. In a community based game, there is no greater punishment (imo, at least from a psychological standpoint). On the left-hand side of your name, you've got a little icon that indicates if you're a newbie, a visitor, a GM of some sort, have a bazaar up, are LFG, in a linkshell.... so how about on the right-hand side, we introduce some new icons? A little gil icon to show that you've been caught and punished by SE for buying gil... a little pitchfork/rake/hoe/shovel/whatever icon to show that you've been caught and punished for selling gil (the icons cause... y'know - farming)... and little running man icon to show that you've been caught using warp/speed hack/whatever movement based tools... then we can even go into a little fish for fishing bots... a pickaxe for mining bots... a hatchet for logging bots, sickle for harvesting bots (do people really bot this other stuff? It doesn't seem very profitable... but I spose it should be included)... an angry black bomb for claim botting/etc/any misc thing I didn't think of...
Do you really think any of those people would even make it to strike 3 in a three-strikes-you're-banned system for "minor" offenses? (I'm assuming here that there's some sort of hierarchy of FFXI "sins", because you're talking about frequent gil buyers, but never mention one-timers, I've seen caught hackers get several 3 day suspensions without being banned, and I've seen people banned on first offense...)
And I know that policy dictates that GMs are supposed to be invis all the time. Hell, anyone who's tried to beg a GM screenshot off of one at the end of a call has been told this. Why? 24/7 GM presense at known trouble spots will do more good than an 'always invis' policy. It doesn't even matter if they're dummy GM's that aren't being watched constantly - I'm 110% positive that SE can alter their GM client to alert an employee of a pending NM spawn, etc, so that they *can* be there to watch. And, as the visible RMT gathering in places like Ulli camp tend to drive out the legitimate players, so too will the visible GMs drive out the RMTs.
And lastly, because it's required to tack on a truly bad idea: Tattletale darts (because I like the concept of darts >.>) and naughty points.
Each month, you get 3 darts per account (not per character). When you see someone doing some suspicious behaviour, you toss a dart at them! /tattle <naughtyperson>! You get a message like "You have tattled on <naughtyperson>. You have 2 darts remaining for the month." Every time a player gets hit with a tattletale dart, they gain one naughty point. Restrict it so you can't tattle on the same person more than once in a month. Then, at the end of the month, you tally all the naughty points players have acquired, and keep an eye on the ones amassing an above-average number of naughty points :P
Hell you could even just flesh out the /tattle command with some nonsense like /tattle <naughtyperson> <reason> - /tattle <naughtyperson> fishbot would let whoever's amassing the data know that you think that person's a fish bot - and how many times they've been tattled on for that - if enough people think they're a fish bot, maybe it's worth looking into? SE does have complete access, after all, with the logs and such to be able to cross reference red and yellow flagging activities (yellow would be like being on 24/7 and not moving - you could be legit & in Rolanberry, red would be like warping from a zone entrance to exit and attemping to zone out 5 seconds after arrival, when the game should know it takes at least X:XX long to navigate the zone through the quickest means possible legitimately - yellow could be iffy dependant on circumstance, red is like a big, glaring "I'm cheating!" sign)
And to cap off the bad ideas. {Yes, please.} become the Special Task Force Unit. And make sure when a STFU GM nails someone, that they have a clever catch phrase like "Your account has been investigated and reviewed and we are now acting in compliance with STFU policy. *Permaban!*" Although, honestly, it's probably only amusing to us English speaking folks... T_T
Edit: Holy messed up italics. My bad.
Edit: And in response to everyone slamming ideas for SE to control their own "RMT" trading, I give you... http://stationexchange.station.sony.com/
Edited, Today 11:40pm by Arketa