Not only about trust. He was attempt to buy merit, you will find his trust rating.
Merit trading is looked down up and will be marked with red. Does it really matter any more? He has been negged accordingly. But trust has nothing to do with ban. Trust is no moderated.
The main reasone for ban his language. Check his profile for that. Always use bad language and pollution this forum. He must be bad due to pollution prevention.
Trolling or using bad language has also nothing to do with ban. If you want to know about what things can lead to a ban you can check the thread on Meta about it. Using bad language will end you in bad situation in front of other but they would not be banned for it.
As far as "Prevention" is concerned, you can add him to your "Ignore" list.
Close this thread as it has served it purpose and your question has been answered.