Once a book gets wet, it’s likely to develop mold. Even if its now apparently dry, some damage has already been done and you generally want to avoid them all together. A dousing also is a lot more obvious than a book that’s just been kept somewhere damp for a long time. When you’re quickly perusing a large pile of books and deciding which to take, you often don’t want to devote the time to individually opening and examining each one in detail. First you want to make a quick cut, then take a second look.
These are tip offs that you should either take a a little closer look at a book or immediately move it to the “no” pile. Once you’re skilled at this, you may be able to sort books as fast as you can pick them up. These are tips for when you have hundreds, or even thousands of books to sort through to decide what you want. Unless it’s something you KNOW is still worth buying even with water damage, these tip offs will general land a book on the reject pile right away.