You will want to wash your chickens before fair time. there are some articles on the internet about this.
but basically you want to make sure its a warm day out- not cold and windy. have a tub with warm water. to get them wet.
a tub with soapy water. not too much soap. last year we used some johnsons baby shampoo. if you get too much soap on them, its hard to get it all out.
and warm rinse water. then we dried them with a clean towel. and then we used a blow dryer on low setting to fluff them up.
do this 3-4 days before the fair. make sure they have a clean pen to go back into. and then clean the dirty spots of the cage out dailey.
because we have japanese and there wing feathers touch the ground. we try to just do touch ups on just the dirty spots of the wings or the birds before we take them to the fair.
clean there toes, etc. old tooth brush is good for this. and try not to get there head too wet.
all the birds that go to the fair are supposed to be healthy, but its difficult to know whos bird yours will be next to or how they handle the stress of 1000s of people and kids looking at them and poking and touching them, or the heat and weather extremes.
Last year we took birds to the fair and when we took them home we quarantined them from the rest of the flock.
a few got sick and we lost one. so this year i am going to give them all vitamin water before we send them to the fair. and maybe some medicated feed before hand.
but not sure.
there are a lot of variables. but just make sure your birds are clean and healthy before going. and don't put them straight in with your flock when they come back.
also get them used to a smaller cage pen if you have one. they will be in a cage a fraction of what they are used to being in and that could be stressful for the birds as well.