We all have read a book in our life and the purpose we do that could be from learning from it, enjoying the story or plot, or even just to say we read that book. I am well aware that most people on this site do not trust books, at all, about magick. Claiming that all of them are fake and out there to get money. Yes there are some books that are out there just to get you money, like scams of "How to be rich!" or "Diamonds, homemade" (those may or may not be real).
I understand your argument, 'better do it yourself than to read it from someone you do not know.' One after someone says that nearly everyone in the room agrees with them because it sounds right, but it is only half of the truth. My question is, how do you do something yourself without learning how to do that trick? Yes you can learn it by listening to someone, aka a teacher, to do it. But on here, online, that teacher isn't going to be able to watch you do your trick. The only thing they can do is give you tips and encourage you. Online, it is nearly no different from reading the same trick from a book. And if you do get stuck, you can either read the book more to get a better understanding or do some research online, other books, or asking people here.
So books, they can be useful by reading it so you can know what trick to do yourself and see how it goes. If it fails for the first time you do it, research it some and see what mistake you have done. Write down what you have done including any changes from what the book has. If everything you have done does nothing but result in failure than you can either keep researching to make it happen or move on.
Books also have knowledge in them. Theories about magick in so many different ways and even what magick is. Again, better to do it yourself than to read it from someone you don't know, always get people discouraged about getting the book. But how do you know it is false unless you read it? Just by looking at the cover? The name? There really isn't a full prove way of knowing until you read it in some degree. If you do not feel like you are learning anything than it isn't worth it. But if you do get the book and have read it all, you can do some research (lots of research you need to do with magick) to see if they are on the ball. Of course asking people on here about something will give you 20 different answers from 40 different people.
In short sums, books are there for a reason. You can learn something in a more isolated area than on this site with so many different views and even limited views (like when someone asks what color is magick and the only answer they get is "It is colorless") of magick. Books, yes depending on which one you get, will give you a more clear, explained, version of what the book is about. Than you can go off and see if it is real with your research and testing.
Bookstores will most likely sell beginners and even lame books unless you go to a magick shop near your area.