In my limited experience running a public TMW server, a small IRC network, and a forum or two I've noticed a few things.
Scammers travel in packs. If there is one in a house, most likely their brother/sister/friend/etc originating from the same location will see all the fun they are having and try to follow suit. Easy to block. Block em for a week and let them mull it over, work it out themselves.
Contrast this to griefers/trolls, who tend to travel alone (when not in their mom's basement). These guys are either very easy to block, or bloody persistent.
The approach I use involves a slow escalation of countermeasures. The simplest one that's effective is what stays in place.
- Make fun of them. It may seem unprofessional, but it lightens the mood and occasionally causes them to desist
- Ban them from the server using standard methods.
- Ban all accounts associated with their IP from the server
- Filter their IP address
- Filter their subnet (depending on just HOW dynamic their IP is. 1 min grepping logs and using whois can tell you)
- Filter out traffic from their ISP within their geographical area using a GeoIP DB
- Global Thermonuclear War
