Salam alaykum
Scholars from the Salaf have stated:
"This knowledge is religion, so open your eyes and see from who you are taking your religion."
And this rule should be applicated in our life, if we want to trust to a muslim, we have to see how this muslim is. We have to see its salat how it is, how much knowledge does he have in Islam, its commitment in Islam, how is its behaviour and so on... We are based o its appearance, because we can not know what is inside the heart, we can not know if its heart is sound or not...
'Abdullah ibn Mas'ud -radiallahu anhu- said:
"People will continue to be in goodness until they take knowledge from the scholars, from those that are bigger then them and from their old people. Whereas, when the knowledge will come from young people and from light-minded, they will be ruined."
I ask Allah to give us shrewdness and knowledge in our religion, then act upon it, call the others sincerely into it, and bear insults and offenses by patience.
Assalamu alaykum