This idea of 'bettering the breed' really troubles me. Breeding to 'better the breed' (in the sense of making it look more like the current breed ideal) has been one of the factors pushing up average COIs, because so many breeders, seeking that perfect earset or whatever, have used the same sire. Rather than Joe Average-looking Dog and Fred Average-looking Dog and Bob Average-looking Dog and Twinkletoes Fab-looking dog being used four times each, Twinkletoes is used sixteen times ( or more...). His progeny look even better, so his sons are heavily used too, and before you know where you are, virtually every line in the breed has Twinkletoes in there somewhere. And there's this peculiar new health problem too...
'Bettering the breed' can mean breeding away from conformational or health disasters, or improving temperament or working ability, and in that case I'm all for it - but you must do with an eye to the overall impact on the breed. And any sane breed club should be prepared to admit that sometimes it means an outcross.
As for where you find a decent breeder, as @BorderlineExperimental says, it's not where they advertise, it's who they are. I've known a thoughtfully bred and well-reared litter be posted on ChampDogs (and I don't know many breeders). Advertising there doesn't mean that they didn't have a waiting list of three or four people, and aren't keeping a puppy themselves.
Working puppies are often found by word of mouth, but not always. And word of mouth might only be, 'I know this bloke the other side of Cambridge, his bitch just had a litter, nice dog, works lovely, he's a good bloke, handles his dogs
nicely, nah mate, haven't got his details, look up the advert and have a chat...'
If you go the advert route, read it carefully. If the bitch is in pup, ask to meet her asap. Look for photos of the owners doing stuff with their dogs. If the puppies are born, see photos of their early days and make sure the background and the bitch are the same as the background and the bitch in front of you.