I've never seen a handbook that led anyone "wildly astray". They're put out by major academic publishers (Oxford, Routledge, etc.) who hire (publishing) editors qualified to select qualified (academic) editors to select qualified chapter contributors. It's not like they're randos self-publishing or something.
The entire point is to be a fairly neutral, comprehensive state of whatever field or subfield the handbook covers. And they generally do a pretty good job. A place like Oxford is never going to publish a handbook that's trying to push some ideological agenda and ignoring half the field.
But if you don't trust the senior editors at major academic presses, then I don't know what to tell you.
And since you've never heard of handbooks, see my peer comment with links so you can see they exist. :)
People on the academic oriented degrees tend to use them a lot. But industry oriented degrees tend to stick with textbooks. (By the way, yes, textbooks are the other kind where you can find wisdom. Normally in an easier to get, more condensed form, but of an older kind.)
About who selects the books, well, who tells you if a book is any good? Some have very radical untested ideas, others stick to older but proven ones. You decide what book to get.
Are you from the EU? Becuase having been in US STEM graduate programs in 2 different fields I have never come across such a handbook or know anyone who has. It's certainly not common in the US.
But more concretely, you can just look up the authors that contributed to the handbook and if you do indeed have a degree in the field, you'll probably recognise them and their affiliations and will be able to know (or at least look up) what tradition they belong to and what this implies for the handbook.