Books, like general commodities, have costs. So the discount is generally not too low. If it is really low, there are two possibilities:

First, books are unsalable, and they can't be sold after being published for more than a few years. It is necessary to clear the inventory. Selling waste paper is also selling, so it is better to sell it at a discount.

Second, books are pirated books. Pirated books don't need to pay the manuscript fee and don't need editing and proofreading. The cost is lower, so they are cheaper.

But we still advocate protecting the legitimate rights and interests of authors, respecting the work of editors and publishers, and resisting pirated books.