I agree with Vela- especially that you do not see that most of these pups at pet stores do not even make it to the store. Last year- a trailer of pups were all dead by the time they got to the store from the trailer being too hot. ( I will see if I can find the link) .
As far as "pure bred"- there is a difference from in-bred, to line- breeding and my opinion is that unless its for a working dog, only dogs that are good representatives of the breed should be considered for breeding- and even then that is a streach. In-bred means like litter mate to litter mate ( brother to sister), and line breeding is within the line meaning a great grandmother, aunt etc. This is done to bring out a good trait- to make the trait dominant ( like a better coat) but still of course- its still a risk you could get the opposite side of the gene just as easily. Even with the best planning, you can still breed two champions together and get " pet quality" pups. Breeding is flat out nerve wrecking- and alot of prayers.. lol. Hoping for months- and watching like a hawk for months as the pups grow. Its put every grey hair on my head, weaked joints in my knees from sitting at the whelping boxes for months etc.
IMO- unless you plan to show- get a pup from a shelter. Someone has already " washed their hands" of the dog, unlike a petstore that is for oppotunistic bas*ards that are trying to make money off the profit of another animal- with no regards to where the pups go ( tell me what pet store does any checking at all in who buys the pups????), or how the dog will be treated etc. The humane societies here do not let a dog go home with someone that day- and do house checks. It doesnt cover everything but at least there is an attempt to make sure the pup/ dog/ kitten or cat has a forever home..