This is a big question - the question of discernment; that is perceiving or feeling the difference between Good and that which is destructive of Good.
When it comes to people in our personal experience, if they are obviously nasty at first encounter then we might well try to avoid them in future - but there are those whose intentions are malign yet who 'charm' us, or place us under a kind of glamour - or upon whom we 'project' good qualities for whatever reason...
Then it is usually time and experience which provides the correct answer.
Mostly, however, it is advice - we accept the judgement of others, and avoid X or follow the teachings of Y because we were advised to...
But which 'others' - who advised us?
If most advice is followed back to its source, we cannot find a source or else the source cannot account for the basis of his judgement. The source is often the Mass Media - which is 1. evil and 2. a source founded neither in common sense nor experience but unfounded assertion.
The path of wisdom is, I think, to ignore all advice except when its provenance is known and approved and relevant.
However, this is considered an aggressive act. There is a general expectation from the givers (or inflictors) of advice that their advice be followed - or if not that you should be able to provide some 'good reason' for rejecting it.
The reality is that all advice should be rejected unless there is a good reason for following it. The opinion of some 'random person' is worthless at best and may be actively malicious.
This is the case across the board. The fact that somebody is your manager, or has a job as a scientist at a famous university, or whatever - means nothing in and of itself - or should mean nothing - unless you have decided that this provenance is authoritative.
This is particularly relevant to 'research'. My conviction is that published research means nothing. We have zero obligation to 'believe' or act upon published research - because published research is of zero intrinsic validity.
The modern world of professional research is full of careerism, status-seeking, money-grubbing hype and spin - in other words the world of research is essentially dishonest; and why on earth would anyone believe anything which emanated from a society characterised by dishonesty?
There is no obligation upon us to provide 'reasons' why we reject some or another bit of research - on the contrary, there would have to be solid reasons for us to accept it. We do not have to prove the dishonesty of 'researchers' by specifically documenting and testing their statements - on the contrary they have to prove their honesty to us.
When we read a Mass Media report of research the problem is compounded - the Mass Media is orthogonal to truth - what they say has zero detectable relationship to reality - so a media report of science is invalidity squared; an actively dishonest account of essentially dishonest communications...
In a world, an environment, which we know is permeated-with and motivated-by dishonesty - the default must be disbelief - and a disbelief far more radical and wide-ranging than usual.
Actual lying is obviously a big problem with the Mass Media and some individuals such as politicians, officials, managers, administrators, advertisers, sales and marketing people and bureaucrats generally - since these are compelled to lie on pain of losing their jobs and suffering other harsh sanctions.
But many or most people will be as dishonest as they can get away with - for example they will say one thing in order to make you believe something else, by choosing their words carefully - and in order to make their dishonesty deniable; and indeed to blame other people for having misunderstood them.
This is perhaps the biggest problem in modernity, deniable dishonesty - and one cannot always be on guard. And people and organisations express a great deal of self-righteous indignation when they are disbelieved on the basis of their known track record of selectivity and false emphasis designed to mislead - the attitude is:
'Just because we often lied/ distorted/ selected/ hyped in the past doesn't necessarily mean we are lying now!" - and on that basis we are supposed to believe them.
Yet the right to be believed is, properly, something which is earned, over time, by truthfulness.
Aside from truthfulness, there is wisdom - which is rare; and there is motivation - who is well-motivated? Because it is only worth listening to people who are well motivated.
How to we know this?
Time, and the heart. It is relatively easy to fool and manipulate people in one short interaction - especially when the content of that interaction is controlled by the manipulator. But repeated, and free-ranging interactions, with gaps between, can reveal many examples of deception - and provide something of an antidote to charm and glamour (especially if you witness the charm and glamour being deployed on another person - or switched on and off!)
This is why in traditional societies teaching involves prolonged and unstructured and multi-situational personal contact between master and apprentice - nobody can keep up an act under such conditions, so people get to know each other.
What of modern conditions? Something similar applies. Frequency of interaction across a wide range and over time - and judging with gut feelings, the head and - most importantly - the heart: these are ways in which we come to know, and perhaps to trust, another person or institution.