Everybody hates exhibiting at trade shows. What a pain. It's expensive and disruptive. Even attending a show in another city is a huge nuisance.
So: someone who lives in a trade-show city (almost any big city) could rent a booth and represent several principals, four maybe for a single booth. Do a little homework, display their stuff, distribute their literature, hand out/collect business cards. Charge a little extra per lead. It's like being a sales rep for three days. Make maybe $1000 a day for part-time work. Use tricks to get attention, like attractive women reps, give-aways, whatever works.
Then franchise it!
There's an inverse function that could be added or substituted into the service: represent multiple potential sellers and walk the floor of trade shows looking for customers among the exhibitors. Again, just make contacts that the principal can follow up on. Charge a fee, $200 maybe, plus more per contact, $20 or so. Don't just collect cards: quality will get you repeat customers. Sign up 5 clients and make $1000 a day just by walking around and talking.
I'd sign up for services like that. It would allow me to be represented in a lot of trade shows I'd otherwise skip.
John