For example, there are famous relationship experts that have written popular books that have gotten divorced, sometimes, more than once. The first question would be if divorce is a sign of a failed relationship. Getting divorced does not mean that a person is a failure, but it does mean that the marriage was a failure, otherwise when people get married they would say something like "I agree to be with you until I no longer feel like it", instead of "Till death do us part".
So, how can it be that somebody that is writing books, giving speeches and advising people on a daily basis about how to have a success marriage can get divorced? Isn't there some contradiction there? Maybe this is an example of "Doctor heal thyself".
I guess there is a difference between healing and being healthy, just as there is a difference between teaching and doing. It seems possible to me that someone could be a great healer and still not able to be healthy. So it also seems possible for someone to be a great teacher and not able to implement their teachings.
Everyone has to find their own way. You can base your decision somewhat on what you know about the source of the advice and the environment where the advice is given. I encourage you to listen to all advice with an open mind, of course not so open that your mind falls out.
Use your own judgement and experience to decide if the advice is helpful to you and if you want to follow it.