Also I feel like this should go without saying but don't buy books, read them, and return them to bookstores.
I'm guessing people think "oh, the bookstore will just sell that book to someone else, they don't actually lose any money." Perhaps with the addendum of "they're not technically losing my purchase, since I wouldn't have really bought the book."
There are multiple reasons this doesn't work.
First, bookstores decide how many books to order based on how many have sold recently.
These days, reorders can be submitted and shipped very quickly, while space and funds are at a premium, and the number of available titles is massive. So it's more cost effective to buy just a couple copies of most books and reorder when 1-2 of them sell.
This means that by the time you return your book, the bookstore may have already ordered more copies, expecting that if your copy sold, there must be enough demand for more. (Especially if it's a new release.)
But in smaller stores especially, a lot of books may ultimately only sell a couple copies, because the number of titles publishing every year is so huge. So the bookstore could very easily end up with additional copies of the book you returned that don't sell, because your purchase signaled a demand that doesn't exist. (Since, you know, you weren't *actually* willing to pay for the book.)
And what happens to those copies if they don't sell? The bookstore can usually return books to their publishers and receive credit towards future orders. But it's vital to note that this doesn't make the store any money, just helps cover its losses. And it still costs the store more than if they hadn't bought that book!
That last piece is crucial. Yes, the bookstore typically gets credited 100% of what they paid the publisher for the book they return. But the bookstore usually still pays the cost of shipping on the returns (books are heavy!), and there are significant labor costs involved in selecting, sorting, and packing books for return.
(This was 60-80% of my previous job. It's a damn complicated process that requires a lot of specialized knowledge and experience to do well. It's full of headaches, not to mention inherently Sisyphean. I miss it SO BAD.)