Pure bread labs are dogs that can trace their liniage through registration with the Canadian/American Kennel Clubs. Along with the application for certification health records must be supplied that state the degree of inbreeding of the litter and results of screening tests for things like hip displacia, heart defects and eye problems. Also they usually come with guarantee against those conditions for the first few years of the dogs life, as by then these problems usually show themsleves.
As the cost of registering a dog after the health check is about $30 I would be wary of anyone who indicates the parents are purebread (ie registered with papers) but the pups are not. The cost of a registered dog can be several hundred dollars more than non-registered, as it is an indicator of a planned breeding program that produces good genetics and health. So if the dog is purebread they would be crazy not to get the papers. In addition reputable breeders can breed for temperment, hunting ability, or show characteristics. When researching a breader it is also helpfull to find out if they do show the dogs, or participate in field trials. If they do their reputation will be known and with a little research you can find out what you need to know.
That being said, i've had several wonderfull pets / hunters that were not purebred, and were of good temperment and health. So it's kind of what your budget is for the dog, and your willingness to accept certian risks for a lower priced dog. Just don't want to see anyone get burned. Just remember, if the dog does not come with papers it is not purebread and the price should reflect that.
Here is a pic of my current buddy "Bralex's Bomb Of Battersea" aka "Cadbury".
Attachment:
Caddy.JPG
4 years old, strength and energy to burn, loves to hunt and make new friends. Can be mischevious.
Good luck in your search.
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Bruce Ogilvie
"Fish Hard, Hunt Hard, Live Hard"
http://www.muskiescanada.ca/