The ability to finish with good condition is largely influenced by genetics. Diet is a secondary factor. When you feel your rabbit's body, the flesh should feel smooth and firm. The fur itself should be soft, shiny, and even in length. Loose or excess skin, a dull or rough coat, or molting coat is poor condition and would be faulted on the table.
Ideally, the pellets you're feeding should bring out the best in your rabbit's condition. Obviously during molts, their condition will be off a bit. But if the rabbit seems to be constantly molting or constantly in poor flesh or fur condition, you might consider a feed change.
If a rabbit is just coming out of a molt or needs a little push, some people will sprinkle black oil sunflower seeds, oats, or calf manna to the top of the pellets daily for two weeks before a show.