I'd say check it out with reservations. I go to a local fair to pick up food but the fair also has birds, cages, food, toys, toy parts, etc. 2 tiels & 2 gccs came from this fair with no health issues but I'd highly suggest you are careful about handling any birds. Most people have hand sanitizers at their stands and ask that you use it before handling any of their birds. Change as soon as you get home and throw everything into the wash.
IF this is your first fair, I hope it is a nice one and that you enjoy yourself and see birds you don't have.