The first sale doctrine gives you the right to resell a book, movie, video game, computer disc, or other physical copy of a copyrighted work. (Note: May not apply to software in Missouri.)
The book is yours, no matter who wrote the words inside it; they can’t stop you from selling it. While it’s true that you’re “making money off of someone else’s work”, that’s true any time you sell something that you didn’t make yourself - if you sell your Honda, you’re making money off the work of all those Honda engineers, but it’s perfectly legal. The bookstore made money off of someone else’s work when they sold you the book in the first place.