"Pedigree" or farm dog - which is best?
Don't believe for a moment that a dog must be ISDS registered to be any use as a sheepdog. This is complete nonsense and anyone who says it should be ashamed of themselves.
There are fantastically good non-registered sheepdogs - some of which would be perfectly capable of winning the top sheepdog trials championships in the world . . . BUT as a beginner, you'll have a better chance of getting good results if you buy good stock.
You may save a few pounds if you buy a pup from a farmer down the road but you could be buying trouble. In an ideal world, you'll take the time to watch dogs at trials, talk to the handlers of those that appeal to you, ask about their breeding, how they responded to early training and observe their temperament.
Anyone who tells beginners that a dog must be breed registered to be any use as a sheepdog, should be ashamed of themselves
Buying an ISDS (International Sheep Dog Society) registered dog does not mean you have a natural winner, it merely means the pup is from proven working sheepdogs.
In reality, you'll probably go to look at the nearest litter the first weekend you decide you'll buy a dog - and almost certainly come back with one, in which case, temperament in the bitch is paramount. But if you're serious about training a herding dog, it's a good idea restrict yourself to registered stock unless you know for a fact that both parents are excellent workers.