Usually the ban is the first warning. I sometimes PM users giving a friendly warning but can't do it for everyone as it's very time consuming and sometimes they don't listen anyway. Though it may seem harsh I think the best course it to learn from it and put more effort into making relevant posts on their return.
I am first time going to praise the MODs for this action as I used to always feel that the forum is not being moderated due to the amount of spam/scam taking place here.
It's a request to even check the Digital Goods section where people are openly selling fraudulent goods, Amazon accounts and even their bitcointalk account. It's illegal and such topics shouldn't be created. I have recently witnessed a case wherein a Hero Member with positive trust sold his account and the buyer was a fraud who went to scam another person who sold him a product just because of his stats.