How can you tell who is an expert in areas that you yourself are not an expert?

It may not seem like  a big deal but to me it seems an important question whom can you trust about a field you know little or nothing about?There is an essay by Steven Dutch about this. [Actually in his writings there are two essays about this. Who is an expert? and how do you discern an expert?] 
There seems to be a few focal points. And there is also a question of subject matter. An expert in Physics today is not the same thing as an expert in philosophy. In Physics, the more one knows, the more expert they become. In Philosophy (or in things like pseudo sciences like psychology), the more they know, the more stupid they become.

At any rate, the  focal points are: (1) Experts. (2) Talented amateurs, self taught. (3) Being yourself self taught--this was the old American value given birth to by the Old Frontier life style. (4) In yeshivas it is assumed if you know Torah fairly well then you know everything.  (5) Public opinion.
(6) Credentials.
My Dad (who made a lot of money on the Stock Market) said the best way to lose money in the stock market is to follow the advice of experts.

John Stossel had an opinion piece about this a long time ago. And Dr Dutch noticed that real experts when they venture into others areas seem to forget that those other areas also require many years of efforts to master

In any case each of these areas requires a whole essay in itself. The USA once was very much into the "self taught" thing. Later "experts" became the thing. After that "credentials" became the thing.

George Fox had the idea of listening to ones close friends and family is the best way and this has support from the Arizal {Isaac Luria.}

This above essay is just to give a brief account of the issues. To me it seems I never found out a good way to decide who is an expert. I had great parents and great teachers in high school and later in yeshiva and at Polytechnic University in NY. But all of that was simply a result of God directing me in good directions, not personal choice or any abilities of discernment.

When given a choice I usually choose badly. Only after a long time would go by I would see how my own choices tended to ruin everything. 

Sometimes the subject matter make the question who is an expert very easy. For example in Physics or Math we have no doubts. The standards are well established. There is no way to fake it. In other areas the subject matter makes knowing who is an expert almost impossible. And there are areas that are in between these two extremes.

The way in moral values seems to be simple. You start with prima facie evidence. The reason is that all reasoning starts with prima facie evidence or common sense principles. Then you work from there. If your conclusion is highly improbable based on some prima facie A then you have to decide which to reject A or B.  It seems to me the Ten Commandments and the Golden Rule have prima facie validity. It would take something with more more prima facie validity to overturn any of them. And nothing can fulfill that condition. 

In any case since I have no idea who I am writing for let me try to be ore specific. For example at the Mir Yeshiva in NY the very idea of credentials was laughed at. Everyone knew that to have ordination was a guarantee of being an עם הארץ (totally ignorant of Torah). They way they knew who was an expert was that they themselves were experts and they had no trouble of telling whom was the best. That was obviously, Reb Shmuel Berenabum. 

The thing that all this leaves out is the fact that there are plenty of people who have something to gain by pretending to be experts and giving themselves credentials.   (That is they give to members of their cult, credentials. And most people are easily fooled by this trick.)  You need the ability not just to tell who is expert but also who has the most to gain by fraud and pretense.  

In any case the Lithuanian yeshiva world is generally very accurate in their assessment of the level of people. The great Roshei Yeshiva as a rule are in fact very great. Rav Shach, Rav Kinevsky were in fact very great Torah scholars and great tzadikim.