It has been my experience, that it is best to have others with an educated eye and hopefully with much more than the breeders to critique the pups.
Critiquing pups at 8 wks, is a long slow process lol, its not something that is done with a hour or two.
It is also not uncommon for breeders to run on 1 or 2 pups that are 'picks' with a wait and see attitude. The breeders that I have dealt with do quarantee a show pup if that is what you have paid for, which means if the pup that you purchased isn't show quality, they will replace it. A breeding quality pup to me is a pup that has no major faults, will show/work and is a very good example of the breed, which also allows you to breed such dog with the breeders permission. Pet quality is generally a pup that has a temperament issue (shy, tender etc), conformation fault, movement fault, coat etc.
A novice person wanting to get into showing/performance etc really should allow the experienced breeder direct them to the pup that they think would be best for them.
I had promised someone once, that they could have pick male in a litter. I made the mistake of sending out a pic of the pups to the people that had already put down a deposite on a pup.
This person, picked a pup from colour ONLY on a 3 wk old pup, for the life of me I couldn't talk this person out of their decision. By 8 wks, I knew the another male pup was the pick and she could have had him..........
The pup she picked, she loves him and that is what counts the most, but she can't do everything that she wanted to with him.............where as the other pup matured into everything I knew he would and its stunning.