Breeders usually classify their cats in one of three (or two) groups: (1) pet quality, (2) breeder quality or (3) show quality. Some combine the breeder/show.
Pet quality means the cat is not top quality according to the standard. This means it may be lacking proper markings (stripes, spots, point color) or the head/body shape is not quite what they want. That doesn't mean there is something "wrong" with the kitten - its just not show quality.
You want the best example of the breed for breeding and showing. So if a person wants to show that cat (or the breeder show) they will want the best examples.
When you talk to a breeder, the breeder will ask you if you want a pet or you want to show - showable cats are about twice or more the price of a pet quality. Say you buy the maine coon as a pet and pay $300. The show brother or sister might sell for $600 or more. Breeders do NOT want their pet cats in the championship or alter classes. It reflects on them and the cattery.
But you can show him/her in a HHP with no problem. Only requirements for that is over 8 months old they have to be neutered/spayed and not declawed (CFA). TICA and ACFA allow declawed but don't encourage it.
When I was breeding rexes, most of them were showable (very good to excellant quality). But most were sold as a loving pet. Not many are interested in showing. But the quality was there in case they changed their minds.
For example, we are waiting to find an ocicat (retired breeder or older kitten) to have as a pet. We are not interested in showing any more (like we did before). Therefore, I'm not gonna ask a breeder for a show kitten, when I have no intentions of showing. We could have had one of the nicest chocolate ocicat kittens at a show. But he was top quality and should do very well as an adult. He also would make an excellant pet - I'm sure the breeder wants to grand him (which he should) and we passed on adopting him.