There is also the breeder's reputation to think of. Lets say I let someone who is a good JRT owner but might not be familiar with my lines OR the sort of dog my bitch produces pick their own puppy.
If it does not work out and that puppy buyer, even innocently, claims that they are having troubles and that the pup is not what they wanted... that hurts the breeder. Not only are you tying yourself to the breeder by getting a pup, the breeder is putting their reputation in your hands..literally.
So if you need to find a breeder that you can work with and trust them. That doesn't always mean agreeing 100% but it means that you have to trust each other on the important things. As I said in the other thread.. I am about as picky a puppy buyer as you will find. And its hard to find JRT breeders who are well versed in what makes a kick ass agility prospect. So I do tell them very specifically what I want. If the pup they suggest is not what I think I want, I would politely decline. Maybe that means no pup for me.. but BOTH parties need to be comfortable with the choice.
That said Seren is totally awesome! It has taken a while to see just how awesome she is but the breeder was totally on the money when he said "I think you will really like this one, she seems like your kind of dog" I was dubious for a while, but being a 1/2 sister to Kat of course I was going to take her. Nope, while she is not Kat she is really starting to bloom into a very drivey extremely happy and fairly dog friendly dog!
So sometimes you just gotta trust that the breeder does know what they are doing...