Limited Networker Field Guide" series.
Name: The Slimy Strong-Arm Salesman
Environment: Hovering vulture-like while hunting or blocking their latest victim from escaping the corner.
Behavior: The Strong-Arm Salesman attends events in order to generate revenue for himself. He knows how to probe for needs, block objections, and make a close like nobody's business. He also has such a bad case of "commission breath" that no amount of mouthwash will make people want to stand near him. His favorite tactic is to lie in wait until some hapless newcomer walks past and then to leap upon his prey and figuratively wrestle him to the ground.
Broken Rules of Good Networking: Events are for meeting, not for marrying. The Salesman can only see his fellow event attendees as so many human sheep, waiting for him to lead them to the shearing. Where the Good Networker views the event as an opportunity to begin a long-term relationship, the Salesman is only looking for relationships which last as long as it takes to get the signed contract. Ironically, if he spent the same amount of effort on creating connections as he does on his selling, he would end up with a network which would feed him contracts much faster than he could bring in by himself.
Counter-Measures: The Salesman is more persistent than the average bulldog. Once he latches on, he won't let go for anything. He will play every card in his hand. Your only chance is not to play. You will probably have to interrupt his spiel, because otherwise his training is never to stop talking for fear of hearing the word "No". In extricating yourself, though, be kind to those around you and don't foist him off on someone else. I would use one of the conversation enders, which you may need to have practiced anyway. You can always use the variations of the "need to powder my nose" excuse. Alternatively, you can "see a friend who needs to have a private conversation".
How We Can Help: As with the Chatterbox, the Salesman doesn't limit their behavior to large events. Anytime they have an audience, they will go into "sell mode". If you want to help them, the first thing you will have to do is break their pattern. If they stop to take a breath (or even if they don't), you can interject the "Oh, that reminds me of..." conversational gambit. Introduce a topic which is only loosely related to what they are talking about (or not related at all -- have fun with it!). Say your short piece and then follow up with a question about them which doesn't allow them back on the sales topic. It might sound something like "Oh, that reminds me about our trip to Disney World last year ... (brief story about your trip) ... Have you done any traveling recently?" If you can interrupt them enough times, they may actually start acting like a human being. After that, if you are feeling brave, you can ask them more about their business -- not their product. Ask about their target market, who they are trying to meet, who they think they can help.
If they respond well to that, then they might even turn into a decent connection. Until then, approach with caution!