I don't know if this is something that could be easily implemented but I think it would be a good idea when a user is banned their sales threads should automatically close and bids removed. I noticed a few sellers in the sites section that have been banned and some users don't realise and carry on bidding when there is no hope the sale would ever be completed. I know potential buyers should be more vigilant and at least exercise some due diligence and check the sellers profile before bidding, but some obviously don't. Just a thought..
There's too much grey area with bans. A ban it's necessarily permanent (it could in fact last as little as 1 hour), sometimes bans are done by mistake and later reversed, etc.
Maybe then put the threads on "pause" while the ban last? That means the threads will show again if the ban is lifted, and if the ban is continous, then they're not a problem?