I agree with Lisa… while your list can be helpful, puppymillers have learned to look very reputable making it much harder to look at the website to determine. The bottom line is, no matter if they sell one breed or more, they can be a puppymill. And there are certainly some very legit responsible breeders with 2 or even 4 breeds! My entry into dog breeding/showing was a woman who had English bulldogs, her daughter had aghans and setters. If they don't have pedigrees and health testing info on the web page, I'd run. If they have it and you check OFA and find they falsified, or only maybe the current or some of their dogs have testing.. run. The rest they can fake or pretend but generations of health clearances generally aren't part of a puppymill.
