Again, Don't go that way!!
When you buy from a breeder you have the chance to see the pups with their Mom and see what her temperament is like, you might get to meet Dad too if the breeder used their own dog. You will have the chance also to meet other relatives to the puppy, older Brothers, Sisters, Aunt's, Uncles, Grandparents etc, you will be able to check out the health of all of this extended family.
Most importantly of all you will be able to check on all health testing done on BOTH parents of the pup, see the relative certificates etc, you will have a much higher chance of buying a healthy puppy from a proven healthy bloodline, a puppy who will have many happy healthy problem free years ahead of him/her.
The pet shop itself may be reputable, but how do you know that the person they bought their puppies from is reputable? You will have no way of knowing if the health certificates (if any) are the right one's for that pups parents, how will you be able to judge the temperament of that puppy, this is a very risky way to buy a puppy, in fact here in the UK pet shops are no longer allowed to sell puppies and kittens any more.
If you really want to show then you are best off getting on the waiting list of breeder with a proven record for producing, sound, healthy even tempered dogs and waiting for the right puppy to come along.