I have been the President of a Bird Club several times and have been part of the management, operation, and visited my fair share of other Bird Fairs and Shows over the years.
There are clearly different levels in which Clubs can manage and operate their Bird Fair and Shows. The vast majority are well run and commonly have an Avian Certified or Qualified Vet inspect all Birds and Parrots at the show prior to opening. This inspection is a visual inspection and all Vendors are well aware that if their Bird(s) or Parrot(s) presents with issues, that individual(s) must be removed from the fair facility. More than three individuals and the Vendor most remove all of their Birds and Parrots. Vendors can and are band from Fairs when there are problems.
In addition to the Bird(s) and Parrot(s), the cages must be clean with both water and food available during the entire Fair. In addition, most Fairs require that the perches are of the proper size for that specific Bird or Parrot. The most common complaint is the size of the cage for mid to larger Parrots. Cages must be large enough for the mid to larger Parrot to open its Winds in at least one direction of the size of the cage when the Parrot is on a perch.
The reality of the Internet has resulted in the decrease in both Store Front and Bird Fair sales. Over the years, I have found that the Bird Fairs have equal prices to Internet pricing, short the close-out /past use by date organizations. Also, I have access too suppliers not commonly found of the Internet.
The down side to Bird Fair and Shows is the huge cross-section of individuals one comes in contact with, i.e. there is no way of knowing what you maybe exposed too. My recommendation has always been, whether a Pet Store, Bird Fair, or a friends Parrot as I enter our home the clothing goes into the wash machine and I go into the shower prior to contact with my Amazon and that has been a Long Standing Practice!