I think that it is really worth thinking about and to find some way to judge the book, as there are good books, there are bad books and there are indeed dangerous books. As one gets more knowledge on the subject, it becomes easier to see if the book is valuable and if it's at least safe to follow it's instructions. I would start with quote from one of the magic study books: "Keep in mind that author is like advisor that you have on the phone, but is far away, while it's you, who is working with a nuclear device. If it explodes, it's on you, while the author of the book might only notice something from safe distance."
Too good to be true
It's little extreme, but I'll mention it anyway despite it being not really an occult book, but for good example. Divine Nutrition by Jasmuheen is a really dangerous book. (she wrote multiple books on the same idea) The book begins by describing how awesome it is to live without eating any food and practically baths you in how awesome it is. Honestly it would be awesome for anyone who is not earning much of money, as food is not cheap and anyone who is counting how much they spend on the money can easily start dreaming about what more useful such money could be used for if they didn't have to deal with food. Then the book gives some exercises and program how to become able to live without any sustenance in 21 days. That's really just too good to be true. Lucky are the people who didn't get lulled by the start of the book into being unable to see it. Some unlucky ones died, following the practice precisely being sure that it works.
Beyond abilities to get the needed stuff/perform the rites
Times change, some things were possible to get in middle ages, while today gaining them or even practicing some rituals is bound to get one in real trouble. Non occult example is that in the past common people were stealing birds eggs so they could raise the birds as their own pets. Or from one occult book a ritual from middle ages (I believe) is called sacrifice of 50 cats in order to summon a deity. It's long ritual with cats dying slowly and definitely not silently. When it comes to collecting material, you can get into real trouble when collecting law protected plants or animals or their parts. You might try to find out the way how you can collect some things. Some stuff can be gained from legal sources, even though you cannot get it yourself from nature. Some things can be replaced, if you cannot afford them or it's problem with the law. Some rites, that could get you into trouble (like those 50 cats) are better to avoid entirely, there are always alternative rites, or modernized versions. Don't forget that even if you are powerful occultist, you are not above the law.
Wrong information
Especially important with herbs, if you read about the herbs that the book tells you to consume and you don't know the herb, always check what it is and if it isn't venomous. Do the research so that the magic you do with the herb is not your last.
Those are points I found so far to be quite important to look for. It's good to start with them, when we explore the book. However it's not all, that is to be considered about the book.
When reading the book, it's good to consider if the author really practices what he says in the book. We cannot often find that out, but a little common sense can give us idea if such a person at least could be able to follow the system that is in the book. With that comes matter of trust. Can this book be trusted to give what it promises? That is definitely easier if the author is/was practitioner of his system.
That should give some basics on when to trust the book and how much. The last I can say, is that you are not author, nor you are his shadow or a copy. You'll never understand it 100% same as the author, so even from that fact your take will be unique. And there is nothing bad about it.
What is your opinion on how to consider if the book is good?
