Interesting thread. Actually, I don't have a problem with a seller claiming to offer eggs or chicks from "show quality" stock. al that literally means is that the parent stock is free from any disqualifications per the Standard Of Perfection.
In the 90's, I raised and showed rabbits on both a local and national level. I would enter 30 to 40 shows a year, and was very successful, and won a lot of Best of Breeds and Best in Shows, while entered in very deep, quality, competition. Over the years, I developed my OWN line of exhibition animals. I culled very hard, and eliminated anything with even the slightest fault, some of them were actually showable, but to my eye, not good enough. Over time, if you are managing your herd well, all of your animals look exactly the same, and culling gets harder and harder.
I would often sell excellent rabbits to other exhibitors, both for breeding and for showing. I was never afraid to sell a good one, worrying about that rabbit coming back to beat me on the judging table one day. After all, I had the source of these animals, and could make as many of them as I wanted. Sure, every once in a while a certain judge would pick one of my "sold" rabbits over one of my "new" entries, but not very often.
I supposed the point that I'm trying to make is the fact that not all of the animals that "big name" breeders sell are pet quality, or have DQ's. If you're doing your job as a breeder, you simply don't end up with a lot of those. If you are buying eggs or chicks from a breeder who is doing well on the show circuit, the chances are that you will end up with some great offspring. Someone has already done the hard work for you. It's now up to you to maintain that standard and strive to improve upon what you have through ruthless culling, and good flock management.
Now that I'm getting serious about chickens again, I'm thinking about showing them in the future. If I have any success, and decide to sell my offspring, I'll proudly offer them as "from show quality" stock. That is, after I do all the work that is required to be successful. JMHO & my 2 cents.