I recently came to a decent understanding of how to weigh out messenger vs message.
Some people say "just because a person is fat and unhealthy does not mean they can't be a good personal trainer or that their information is bad". This is true. In the same way, just because someone is strong and fit does not mean they have great information or technique about how other people can also be strong and fit. However, when a person who does not have a good way of differentiating bullshit from true knowledge is forced to make a decision about whether or not what someone says is true, then they need to look for evidence. If someone is a fat personal trainer, but they have clients that they have helped successfully, that looks good on them when you can see that evidence. But if you can't see their clients, and the personal trainer is fat, then what proof is there that they have any expertise? It seems like there is none. Similarly, if a man in a failing marriage gives you marital advice, unless he can show you some evidence, like a mutual friend who followed his advice and saved his marriage, then you don't have good evidence to believe them. You are taking a gamble if you take what they say at face value.
Both are important. When someone has no other evidence to prove that they have some expertise, then their own personal situation is definitely something we should judge. If their personal situation suggests they're not knowledgeable, I wouldn't fuck with their advice.