Having recently got a puppy from a breeder - here's my experience. Just talking to the breeder made a lot of difference and told me a lot.
For example, my pup's breeder (and her mum!) is a couple of hours north of here. Dad came from a few 1000 miles away - subtext, breeder is interested in improving breeding lines, not pumping out maximum number of puppies.
Another example - in talking about the dogs generally, she was able to tell me characteristics of some of the different breeding lines. Subtext - again, a passion for improving the breed.
Lots of backup, support, and information - she's followed me up since I got the pup, answered lots of probably stupid questions before I got her, etc - subtext: interested in the dog going to a good home, not just in selling her.
Comment about going to Queensland to pick up a puppy, because she had provided a free stud dog to this kennel a few times so now they were giving her a puppy.... you're getting the message.
Showing her dogs - actually finding a time to meet the dogs on a weekend (given that breeder lives 3hrs drive from here) was a challenge because the owner was off to dog shows. Now personally I just wanted a pet, champion pedigree doesn't really excite me - but again, it was an indication of how the breeder thinks about her dogs and that her priority is NOT a puppy mill.
Where the other pups were going - one was staying to be a stud dog. One was going to be a show dog. One was staying to be a pet because her husband likes tan-and-whites. One (ours) was going to be a show dog (when I first contacted the breeder she had no pups available!) until its owner-to-be lost a job and decided not to take it (so breeder contacted me) - now of course the breeder could be lying, but again, I don't get the impression of a puppy mill.
Of course, the breeder was registered - this information is online here. I also found breed clubs a handy source of information.
I spoke to quite a few breeders and some of them are mad as cut snakes (i took to making first contact by e-mail after a while, so I could filter out the stranger ones!). The "puppy mill" ones are pretty obvious - actually sometimes they were obvious from the breeder's own website - the word "puppy farm" on one had me running for cover!
Anyway, I don't know of an "official" way to check, but with this breeder, several conversations, e-mails and a couple of meetings and it just all added up right. You get a sense of their priorities!