I have seen it happen in other posts too, but I myself don't like it. That's just my personal opinion though. I wouldn't want a commissioner doing that to me. If I had an issue with an artist I wouldn't use being posted to A_B as a threat.

Yeah it's a way to kick them in the rear and get motivated, but it doesn't always work. (Example, another artist whom I won't name has been posted here MANY times now, with no change.)