I take a different stance: the scientific method is all you can trust. Word of mouth is also inherently biased (e.g. someone that works somewhere may paint a rosier picture at a moderate enough company due to in-group dynamics or even mild forms of stockholm syndrome, just as a ex-employee might be overly negative, and it's up to us to identify potential sources of biases in these anecdotes and take them with the appropriate amount of salt)

Same goes for online reviews. Even if a scummy company deletes 1 star reviews, there might still be 2 star ones, or 3 star ones that are (in my experience, anyways) more grounded than the more impulsive 1 and 5 star counterparts. A keen applicant of the scientific method would question a unnatural distribution of high reviews with low information density, not because of prior accusations of foul play, but simply because one wants to come up with a reasoned theory of how the dynamics of review systems play out in general. You may not necessarily have hard evidence that intentional shenanigans are occurring in any given review system, but you can still make up your mind in terms of what are likely factors for why reviews are the way they are and how much weight you're comfortable putting in them.