Delete usually means the RMT deleted the char, to make a new one, and get around your blacklist. They usually do this as I've been spammed by the same RMT message by several different names before. And of course, they get deleted a couple hours after I add them.

Ban however, I feel like never. If its in waves then Yoshi flat our lied to us when he talked about housing prices don't include RMT gil "because those accounts are banned immediately", no, they dont. I've seen teleport botters have fun for months. You can go on any botting forum and see how they all laugh at the pathetic attempt SE make in stopping RMT/Botting generated currency.

Deleted > Done by RMT to get around your blacklist
Ban > Once a blue moon probably gets about 20% of actual RMT/Botters.

I don't really blame the GM's work effort, I think there is some really long, bullshit process they have to do in order to process a ban, because if "investigation" is used an excuse again then that is just sad, sorry but you cant do your job if it takes months to investigate a teleport botter.