I'm going to refer you to a sticky here: https://www.dobermantalk.com/breeding...-breeders.html
This is a difficult line. I can only say that each person has to decide what breeder is right *for them.* There's an obvious backyard breeder, where there is no concern for health, no knowledge of pedigrees, no participation in showing or working dogs, and none of us support that.
And then you have the fuzzy lines, where things are less clear, and we all have to decide what it is we're looking for, individually. The information is there on breeders, and we each have to decide what's important to us. Do we have a problem with bitches being bred at 15 months old, for example? Some people do, some people don't. Some breeders breed a lot more litters a year than others (either because of co-ownerships, or not). Some do more thorough health testing than others. This is where it really comes down to buyer research and preferences, and what you want to support. No one can make that decision for you. Sometimes people compromise because they don't want to wait, or they don't want to travel, sometimes people wait years for just the right puppy....
There are really no black and white rules. There's no one "right" breeder for all of us. We each have to decide what we want and what we support, as long as we aren't supporting poor quality breeders that clearly land below the bright line that is pretty easy to discern.
Hope that makes sense.