@Hime @Juji The best and by far most cost-effective way to mitigate bots/adena sellers is making it unprofitable for them to do so from free accounts, or to remove free accounts altogether.
With free to play, there is no capital investment aside from time (which most of the bot-controllers are in countries with very low time-value functions.. i.e. they have nothing else to do) for Adena sellers to do what they do. This is directly a result of the free to play model; combined with the fact that free accounts receive the same adena drops (and nearly the same item drops) as paid accounts makes the problem impossible to enforce from a logistics standpoint, which your team is facing daily.
If you make free to play far less functional to farm adena than VIP, then bots will be forced to pay for VIP, which
Increases your revenue directly. The more you ban, the more they re-create and purchase VIP for. You have direct incentive to enforce them instead of indirect incentive.
It makes them go through more hoops to hide financial information from you,
Allows you to link them together through said financial information (sometimes),
Reduces the problem numerically (increased barriers to entry reduces numbers of firms in the market) to allow your GM team to more easily dispatch of those who are willing to take the risk with the increased capital costs. Getting 9 accounts VIP4 is quite a large capital investment for most adena sellers. It will absolutely reduce their number.
There are many other benefits to pay to play, or to boosting VIP (and reducing free) rates so that they are incompatible and that long-term play (40+) is not plausible for free accounts. This is just one of the major benefits, but it may be the most important one.
If you have a bot-free game you will attract more long-term players than any other business model (free, p2p, p2win, whatever) could do.