Here's another perspective to play with. (amended Sat am)
The core issue in relating to a teacher or other source of input is surely trust. (trust is in essence a description of the most fundamental belief we hold about others - its essentially created or destroyed depending on whether or not actions likely or actual are perceived as more or less loving towards ourselves) Meaning our degree of trust is a measure of our willingness accept vulnerability and/or risk as a result of relying that the actions of the other will be in our interest.
Goodwill/benevolence, integrity/honesty capability/skill and predictability/reliability are often cited as major dimensions of perceived trustworthiness. Where our belief in the likelihood of the others delivery of any of these is damaged, trust reduces.
We tend to particularly emphasise the first two, although the trade offs are individual and complex - depending on context, cultural values, personal conditioning and experience and so on. e.g. westerners often get especially upset about sexual morality. We routinely tolerate deeply dishonest, self centred and incompetent behaviour in politics and business, but may divorce over a single mistake.
We're likewise heavily conditioned to instantly reject especially spiritual or religious teachers that fail to live up to either their own teachings, or who break our cultural taboos.
Yet trust is not a yes/no decision - the possibilities range from walking away at one extreme, through various conditional judgements, to trusting beliefs and affect/empathetic or loyalty based trust at the other.
In life we'd be unable to function, and would lose enormously if every time we felt the tiniest bit suspicious or let down we walked away and refused to have any more to do with the other. That's not to say that there are not absolute truths, but these are of a higher nature, and inexpressible/opaque to intellect. The situation in relative reality we live in is not that simple.
In life we actually proceed by finely nuanced assessments of at least the multiple variables out lined above. We use these to decide how much risk/exposure to accept in a given situation.
The decision framework relies on only bits of data and our system of belief, and as above these are also highly complex and unreliable.
Perception is at the centre of all of this, and it's clear that perception is not the most reliable of judges. It's equally clear that judging is not a good idea - when we adopt a default position regarding anything we close down all rational process in favour of what is only a personal belief - one probably based on very limited information.
It's not hard to get turned against a teacher. Possibly out of some of the above reasons - some of which are valid, and some not, or perhaps simply out of not understanding what the teacher is trying to do. Its pretty much a given that all teachers are perceived (whether or not this is the reality) by many people as making errors. Teachers that appeal to mass sentiment are in fact almost by definition pushing a lower view.
The truly great teachers are often only understood in retrospect, or become the target of popular hostility. The highest view is rarely the majority one, and is in fact going to be downright threatening to most.
So is it realistic given this complexity to make digital yes/no judgements on teachers based on single as we see them 'significant' bits of data, and hence potentially to reject whole bodies of useful teaching and other material out of hand?
Is it not possible to proceed more cautiously, using our own discrimination as we go and witholding the head over heels commitment many seek until we've gained a lot more experience with a teacher?
Is it realistic either to seek to fix personal perceptions and/or beliefs as truths, to judge rigidly by these and to demand that others believe as we do too?
Is it not possible to have some reservations about teachers, while at the same time drawing on their output where it intuitively feels right/is helping us?
This all of course implies a requirement for intuition and wisdom, and that we need to be cautious as these develop. That we will make potentially serious mistakes is a given. But that's the learning process, the means by which Spirit teaches - on the basis that intellectual knowledge is fairly meaningless, difficult to integrate and very different to becoming.
To move beyond a very moderate attempt to insulate others from what we regard as false teaching is (a) impossible, (b) more likely to inhibit their learning, and (c) very likely driven by ego - either as a result of an unwillingness to accept the reality, or an attempt to control them...
Given this inability to either easily access absolute truth in this life, and our very limited ability to recognise it even if we find it who else can be responsible for our path but ourselves?