Fair enough question.
Yes, chickens are judged by phenotype and whatever the genes are behind what you see? Well, this is where the integrity and reputation of the breeder comes into play. First, let's deal with the title "breeder".
The vast majority of folks "breeding" are not breeders at all, they are merely propagate birds. They're hatchers, propagators, not breeders. The art of breeding as yes, it is as much art as science, is rarer than what most folks understand. The well known, true breeders of high quality, true to breed Standard breeders are quite rare. There is a popular movie out right now on CMT, Amazon, etc called "Chicken People" which open the viewer to the world of true bred, Standard bred poultry breeding, exhibitions and judging. This is a world that backyard propagators often know little to nothing about. It's worth a look see.
Quality breeders earn their reputation by consistently producing high quality, top notch birds of distinction. They are usually well known in the poultry community that specializes in this hobby/artform. They've exhibited their work at major exhibitions and endured the process of critical peer review such exhibitions provide. If you state the specific breed in which you have an interest, seek out the breeder group for that specific breed through the internet or social media, the top 6 or 7 breeders names will surface immediately. Their reputation is well established and they are well known within that breed's community of devotees.