Shorter workshops are tough. Usually the fair organizers will come around and ask for feedback - but not always in a written way. Truthfully, I wouldn't have time then to respond in writing. Asking me later on a written evaluation would be ideal. Keeping the admission price down for attendees helps too.
Most places offer help and services.
Some vendors use that service while others do not. Also need to know what else is going on in your area on the dates you wish to hold a fair. Scheduling a must. We need to be true to doing whatever God calls us to do. Homeschooling is a long, consistent pull in the same direction.