While it is sometimes possible to breed out bad traits over time by breeding with stock that does not have the flaws, it's generally cheaper in the long run to start with birds that don't have major flaws, whether breeding for show or pet. And it's important to grow your first few hatches out to maturity, taking photos at least weekly, so you can backtrack and see what the faults and good features look like in very young chicks.
I am on my fifth generation of Narragansett and I've worked very hard to retain the exceptional conformation, temperament, and color of this line while working on increasing the size and shank length. A few BQ birds have probably slipped through my fingers when I sell as poults, but I always have enough to choose from. My rule of thumb is to save the best 10% each year for next year's program including the best male under 3 years old. I broke that rule selling one of my cockerels this fall, but he had only 2 of 3 desirable characteristics (color, conformation). His temperament left something to be desired.
Selling surplus birds at point of lay or broiler size is a good way to get a look at the nearly full grown birds to help make decisions about your breeders. Selling to a family member, friend or neighbor works too.