Even though you think your prices are the best at the market, you will find people will haggle you down from 50¢ if they think it’s unfair. Be prepared to haggle and provide counter offers. Instead of taking a quarter for a 50¢ book, suggest they can have two books for that same 50¢. It can get pretty silly at times, but the more flexible you are the better chance you have of selling off all your stuff.
On that same note, make sure you have a ton of change on hand. Cash is great, but you need coins too.