So I guess the answer is... it depends! :lol: On location, and which club.
For anyone thinking about showing -- for almost all reputable US breeders and for many reputable UK breeders, your homing contract for a pet cavalier will almost certainly have specified a spay or neuter by age 1 or so maximum and the dog will be on restricted registration. It is very rare for a cavalier sold as a pet in the US, Canada or UK to be of club-level show quality-- otherwise the breeder would have retained the dog within his/her own breeding program, for showing, or sold the dog as a show dog but generally never to a pet owner -- those who buy show quality dogs are carefully screened or the dog is co-owned precisely because the dog has to remain intact for showing and thus, can be bred. Show breeders generally tightly control who can breed dogs of their breeding for overall breed health and welfare reasons amongst others! Good breeders spend a lot of time choosing and matching pedigrees for best health -- to allow someone to breed indiscriminately would undo all that hard and conscientious work.
If the dog was sold by a breeder who didn't place any restrictions on what you do with the dog, especially in N. America, it is extremely unlikely to be show quality as the breeder is unlikely to have any show quality breeding dogs (despite what she might have said!).
So realistically, a cavalier sold as a pet isn't going to do much in the show ring. I know we all know our dogs are beautiful
-- and they all are for many reasons -- but are very unlikely to have the excellent balance of looks and temperament that go into a show dog. If anyone thinks theirs might, it would be worth getting involved with your local or regional club, get to some club events, and star to learn what makes a show quality cavalier. Then once you get to know some club members, ask a friendly person if they would be willing to evaluate your cavalier and offer an honest opinion. The show world like any competitive arena can be very crushing and cruel and it is better to spare oneself some unnecessary embarrassment and awkwardness by entering a cavalier way off show standard and perhaps being made to feel foolish. That's IMHO but I have been around the fringes of the show crowd enough to know showing isn't for the faint of heart nor the thin-skinned and it is better to take the time to do your breed homework well in advance of ever entering a ring.
The fun shows give many people the chance to enjoy themselves, not feel pressured, learn some show handling techniques and see if this is a real interest or not, and can open the door to getting involved more seriously at club level.
Knowing what makes a good show dog and a beautiful cavalier in show terms takes a long time and generally, you'll need to spend time with a mentor and really study the dogs at the serious shows, having someone explain their qualities and strengths. It has taken me several years to begin to get a good sense of what is valued and I still wouldn;t have any idea why one dog would win over another. But i also have learned enough and observed enough to know that, of the 60-ish or more dogs or so I have homed through rescue, not one would have been close to show quality. Wonderful, lovely dogs, but not show quality dogs. It is all a fascinating area and well worth learning more for anyone with a real interest in the breed and getting into the show world.