I don't show birds and have only been to one show, ever, and that was just to look.
Sneezing alone may be environmental. I have one hen who has sneezing fits from time to time, especially when she eats fast. She's done it for years, has never been sick at all. I hear her over the baby monitor at times and know exactly which hen it is. Ammonia buildup can cause it, too, but you'd be hearing more than just one hen if that was the problem. They can also get a piece of grain up in the nares and be trying to dislodge it, so there are many external reasons for just sneezing.
possumblossum, CRD/mycoplasmosis can be passed down through the egg to the chick; it's called vertical transmission. Some diseases can and some cannot. Best of luck with your flock.
ETA: Philosophies of chicken management vary. Because my hard line stance on respiratory illness is not shared by everyone, I never buy started birds, not even chicks, from individuals, even those I trust. Most old time chicken keepers/breeders will not treat, either. Every person must decide for themselves, based on facts they learn about disease transmission. There are some harsh realities in this hobby, for sure.
