Yeah,

This has been going on for ages not only in Seal Online, some possible solution to this are:

1. Hire a few GMs and assign their job to Banning Cheaters, Gold Sellers & when banning ID/IP/MAC addrs email the cheater with the screenshot (these GMs need to take shifts so that at least 1 GM is online 24 hrs and monitor chat in Elim or just set up a program that save record logs and filter for specific keyword ie. $, sell cegel, sell gold, etc be creative)
2. Make the game PtP