
Infact Lucy, you nearly hit the nail on the head!
Now some handlers having dogs who don't show teeth in breed ring, do train to show the dogs teeth in handling classes (As how can you asses handlers showing teeth if one person doesn't do it?)
On the other hand if they don't show the dogs teeth I would expect to hear knowledge from the handler saying "In this breed the teeth and bite are not within the breed standard and therefore not judged" or something along those lines in a polite mannor and therefore sow they know the breed they are handling ;) If they don't say it polite then they will not be as highly placed depending on the rest of their table and pattern work and of course the competition!
I can think of two handlers who have two different non teeth breeds who have taught their dogs to show teeth, however if a judge goes to do it themselves..... LOL