I agree with Chris, I don't know why anyone would ever buy from an auction. In addition to all the health and quality issues he highlights, there's the potential problem of healthy birds actually becoming infected from dirty cages from the previous lot, and also, a major problem for the birds, the stress of being taken from a quiet run among their own flock, in a vehicle, perhaps a long way, then spending a very stressful day in cramped cages with lots of people looking at them, and the crowing, the noise and shouting. Then another journey to whatever home they've arrived at, exhausted, probably hungry and dehydrated, and certainly very stressed and shocked. Not a good start, and the stress is likely to lead to the emergence of illness, a big risk to the rest of your flock. Also of course, you have no idea of the conditions they've been reared in, and no chance of coming back to the breeder for advice or recompense if things do wrong, I think the same things can often be said about poultry shows, the two I've been to were ear splitting with the noise of the cockerels all crowing, and I felt sorry for the birds.
Best to buy from a recommended breeder whose premises meet your standards, where you can examine the birds in the hand before purchase. Then bring new birds home quietly and keep them in a ready-prepared quarantine run for a couple of weeks. This lets them settle in before meeting the rest of the flock, and enables you to decide if they have any health issues which need dealing with first.