How to find a "reputable" breeder of cross breeds?

I know there is a lot of concern about puppy mills and backyard breeding and things of that such. I read a site that said a "reputable" breeder will usually not post classified ads. I found a dog in a classified ad online that I am considering adopting, I am just worried about supporting a "bad practice." The owner seems friendly and knows what she is talking about. However, she seems to breed as a hobby in addition to being a stay at home mom. Is this bad? It's hard to find a reputable breeder or cross breeds. Any feelings or suggestions about this? Please, don't criticize me for wanting a cross breed or for not adopting from a shelter. We look at the shelters often but want to make sure we adopt the right type of dog for us.