I check reputable breeders on the forum, and typically purchase through contacts made on forums. I know for the fish/salamander's I have purchased an online presence on the forum I use helps quite a bit. I purchased some salamanders from a breeder on caudata.org, and one of my main motivators for choosing that breeder was that he had been known to give good advice, so I know I could get feedback/advice if needed. One issue I have had in the past with online fish breeders is that they tend to be unreachable the second they get your money, so I'm a little more picky now.