First time seeing this, I definitely think there can be both. When I was at TASC I saw a breeder that was going over bird care with a buyer, and not just a little bit, they were going SUPER in depth and really working with the buyer in a way that was pretty impressive and far more than I expected for someone wanting to make a sale. I've also heard of breeders that have gone and will be prepared with pamphlets and refuse sales quit readily to people they don't approve of even if it means taking the bird back home, which again, I really do approve of. The disease thing does freak me out, but I'm also the first to admit that it's a risk with any new bird, but a lot more chancy at a bird fair given the fact that bird might have been at quite a few fairs and its parents, etc.
I also went to a fair last weekend and was near a breeder table that made me so
They had unweaned babies and were selling them, I watched them sell a baby grey and demonstrate to the buyer how to feed, they did it quick, told them to temp, didn't mention anything about hot spots etc, and then stuffed the baby in an open lid carrier and handed it over pretty much saying it's easy to do, they'll pick it up soon enough. No mention of how to wean, or warnings about aspiration or anything else that are very important. The parents pusehd the baby into their toddlers stroller with the lid off and just kept cruising the bird fair.