Especially with our fertile hatching eggs, we have some great lines that produce amazing show prospects. Ours is an NPIP hatchery and our birds are purebred. (The exceptions are designer hybrids, Easter Eggers, and the Red Stars which are a hybrid "mixed breeds" by nature.) Other breeds are pure, but don't have APA standards yet: take, for instance, breeders working to develop APA standards for Svarthonna and some other breeds that are rare to this country. But regardless, in all cases where APA standards exist, our birds are selected to conform to them, and they're selected as well for health and docility. In cases where breeders are working to get APA recognition, we breed to the proposed standards.
For this reason, our birds are often shown, and many times win! 4Hers particularly like that they can order one each of many breeds, so they can have a real selection of birds to show. However, our birds are not bred ONLY for show, meaning physical characteristics are not our only concern. They are bred with the needs of all chicken keepers in mind. That means hardiness, egg laying capability, egg color, friendliness, and so forth are also important. Heck, those things are all important to reputable breeders, too! It's a bad idea to ignore health in favor of conformation.
All that said, no one---hatchery or breeder---can guarantee you'll get a show winner. Even when purchasing from a top breeder of show birds from winning lines, not every chick hatched will make good show material. Even the prettiest chickens may not have the personality for the show circuit. This is why no one can guarantee their chicks are "show quality." The honest thing to say is that chicks may have show potential, or that they come from show lines (meaning mother, father, grandfather, etc, have won shows). Do remember that even top breeders may hatch hundreds of birds from very good lines before they find The One they feel will be a grand champion at a poultry show!
Don't forget, too, that true "show" birds are often not the best layers, as they are selected more heavily for conformity to breed appearance standards rather than, say, winter laying capability. Reputable hatcheries select to APA standard, and breed for health and docility so you have a well-rounded bird for the breed, as opposed to a bird that is selected exclusively for, say, extra dark plumage color but doesn't lay well.
If you're interested in exhibiting your birds at poultry shows, take the time to attend a few before you take the plunge. Shows are also wonderful places for seeing some unusual breeds in person, and talking to people about what their favorite birds are. Someone who wins a show with a Silver Spangled Hamburg, may actually prefer Barred Rocks for a laying flock, so ask around!
Importantly, you'll need to pay extra attention to biosecurity if you're going to shows, since your birds will often be exposed to other flocks, and everything they might carry. Even if it's just you going to the show, you might carry something back to your flock! For tips and advice on this subject, you'll want to watch this YouTube video: