Easy solution for dealing with people who are selling books for 1c online and killing your chances at sales... flip them offline to get better books to sell online.
Talk to a few used book stores that buy books, get an idea of what they're looking for (nonfiction, scifi, classics, etc) and match a bookstore to your supply of books. All the used book stores I've dealt with offer 10% of the retail price for cash, and 20% for store credit. Go for store credit. You can bring in boxes of books from estate sales, garage sales, whatever, and save up store credit for when you find a more valuable book there. What would you rather ship, 100 books for $2 each, or 1 book for $200?
Also much easier to check how much a book is selling online if there's only 1 or 2 books to check each time!
Quick rule of thumb when looking for books to flip: Is the difference between the selling price (at the garage sale, whatever) and 20% of the original sale price enough to make it worthwhile? I'd go for at least $0.50 profit on each book, $1+ is better.
Years ago just before I moved out of my parents house to go to school, I cleaned out my closet and took a few boxes of books to a local used bookstore. I ended up with over $300 in credit.. I used that credit to buy new books I wanted for my own collection, but I could have easily bought a rare book to re-sell.