There are a few reasons to get banned.
The worst offender is the new member that signs up to just spam the board over and over with whatever they are selling. Those types of members get the boot immediately.
If a member continually over and over disrupts the forum fighting with members, obscene language, trolling, and total disrespect for the lawnsite community, then action must be taken.
Fortunately, we have a great bunch of members, so banning is not a big issue here.