Marketing like this can fulfill at least 2 roles. You can be there to make immediate sales, but you will also be in a position to show off your knowledge, skills and professionalism which will help to build your brand image.
Not everyone wants their carpets cleaning this week, this month or even this year, but if there's something about you that sticks in their minds, you're off to a flying start when they're ready. Obviously, these marketing exercises must be researched and focused at your target audience.
IMO, it is essential to have a live demonstration or two. Noise for us could be a problem. The events I have taken part in have all been indoors and I've demonstrated correct vacuuming and spotting techniques. I've done very well out of them. For a county show, a T/M would be ideal or porty with a genny, but try to place as far away as poss to avoid too much noise. If you demo spotting techniques, you could also sell spotters with your name on to reinforce your brand.
Safe and happy showtime
The Ken