Good question and here’s the short answer. You can’t control it and actually, that’s a good thing. I’ve found that most audiences police the tweets and if solicitations come through, the crowd takes care of it. I’ve been using twitter for meetings since 2007 and never had that happen. Some exhibitors may put tweets into the stream but if they overdo it, they get a backlash from the audience. Plus, I really doubt that a business would target a conference sending hundreds of tweets. It’s a waste of their time.