Will there be any insight into who's banned, and for how long?
For example, if it happens automatically, and Person A gets banned, while in the middle of a transaction with Person B, will Person B be able to tell Person A's been banned? Or will they think they're being ignored? This could lead to broken sales, etc.
If it's noted on their profile, or on their posts, that could mitigate some of it (he just stopped answering PMs... oh, he's banned until Tuesday).