The AKC standard is a picture of the ideal Pembroke Corgi put into words. All ethical and responsible breeder/exhibitors attempt to come as close as possible to meeting this standard of perfection with each and every puppy.
Although there are no known health problems associated with fluffies (long coats) or mismarks or whiteleys (degrees of excessive white markings) these issues are considered very serious faults in the breed and so are are never intentionally bred for by an ethical breeder.
Be aware that purebred Pembroke Corgis cannot and do not come in blue merle, red merle or brindle. Avoid the unscrupulous and unethical breeders marketing such colors as purebred Pembrokes. For more information see: Is There Really Such a Thing As A Blue Merle Pembroke Welsh Corgi?