Just looking back over the last couple years of keeping hens more seriously and it's occurred to me that the hens I have been most disappointed with are the ones we bought from so called pro breeders who have retail premises. Our Light Sussex (hybrid strain) have been a disaster. Thin and mucky eggs, won't stay out of the nests at night, poor laying numbers and egg shape. Very prone to dropping dead at a second's notice. The same with the CLB's I bought which look very good but don't lay up to numbers and all show sings of IB which none of our other birds do so I'm putting this down to over vaccination (?). All our home bred mungrels and pure breeds seem to be feisty and strong and good layers to boot.
I now gather that rather than breeding their own stock, a lot of these guys are just buying POL hens from big time rearers who bring in day old chicks from Eastern Europe. From chatting to one such rearer I know, they are more interested in breeding in traits so that birds can be sexed at a day old (even in LS etc) than they are in breeding quality.