I've been trying to think what to post here because my feelings about avaluations are complicated and I agree that people need to know what they're doing - which you learn through a lot of experience.
A person without a lot of experience can still do an enormous amount of good by going to shelters and getting better pictures and sharing their observations. And by doing all that, you will start to gain experience.
I just think it's vitally important that people know what they don't know. And no matter how much experience you get - never get cocky. You can and will be wrong at least some of the time. Leave your ego at the door. A dog's life could depend on it.
The other thing I wanted to say is that I look at evaluations as a continuum. They're a source of data but there's not really a pass fail of some objective test.
If someone is looking for a dog that's ok with cats, if the shelter dog shows too much interest in cats, then you might say that's not a good dog for them, but it doesn't necessarily mean the dog "fails" the eval in the sense that it's unadoptable for someone else.
I have a lot of problems with some of the shelter testing that goes on - I think the focus on regimented pass/fail dynamics and pushing dogs until they react is unfair. It's data. It can be useful to the person thinking about taking the dog. But it should be seen for what it is - ONE technique administered in ONE way. Not the be all end all, dogs on this side of the line = good, dogs on that side = bad. There's a lot of testing that a Retriever or often something like a Pit can just sail through - on average, they're a friendly and low anxiety bunch, but that some of your herders and small dogs find almost impossible. Doesn't mean they're bad dogs, just different strengths and weaknesses.
If we're talking about assessing more than Shepherds, different breeds really do have different quirks. If someone tells me a Chihuahua is snapping in a shelter, I think "yeah, and?" For me that's not a deal breaker, that's a typically terrified little dog. If a Golden is snapping, I think that's much weirder. If a Pointer has gone cage crazy, that's not too surprising for a high energy dog. but if he's lying on the ground completely passive, I'm more concerned that he's ill. If a GSD is barking at strangers who pass his kennel, I don't necessarily think that's a deal breaker when I'm deciding about a dog to pull - being territorial is a common trait of our breed. If another breed were doing it, it might give me more pause.
Know the breed you're assessing. Often the shelter won't. Know the group you're assessing for, their deal breakers will vary.
Also just being in a shelter can have a really major impact on a dog and throw off an evaluation totally, so it's important to keep that in mind. We've all seen the Shepherds who are fear aggressive wrecks in shelters but fine the second they're out of their kennel. But the opposite can kind of be true too. Being in a shelter can really squash down a dog's personality. They can come off as much more passive and laid back than they actually are. I've had MANY fosters who were 180 degrees different from my initial assessment after 2 weeks in foster care. Dogs who test great with other dogs but as soon as they feel comfortable start picking fights. Dogs who seem laid back that are high energy, dogs that seem high energy who are actually laid back.
So, I think it's important the people look at shelter assessments in that context - here's a snapshot of how this dog acted under these circumstances, on this day. It's data but it's not a definitive description of who that dog is.
Different rescues, fosters, adopters, whoever are going to have different ideas about what they're looking for, what risks they'll take, and what they can work with and what they're equipped to work with. When you are evaluating for someone else, all you can do is give them all the information you observed, the context in which you observed it, and let them make the call, but it's vitally important that you don't go beyond what you know and beyond your experience in assessment.