I actually kinda like garage sales where nothing is marked. I gather up everything I want and give an offer for the whole pile. "Will you take $10 for everything?" I've found that often gets me some great deals because they see how much "stuff" will leave their home if they accept it, and "$10 for everything" sounds like more money and is a lot less hassle than if they do the "$1 for that, $2 each for those...50 cents per book times six books..."
Books, in particular...I can walk off with a whole BOX full of books for about $5, if I go late in the day and offer to take the whole thing. People really hate hauling boxes of books back into the garage. I've made offers like that that were rejected on Saturday, but the same offer is happily accepted on Sunday afternoon. LOL
Free stuff - my parents used to have garage sales often, and we'd put out a "free" box but people rarely dug through it. So we changed it to a "Nickle" box and that made people a LOT more interested. I think people assume it's junk if it's free, but if we're charging even a nickle for it, it must be somewhat valuable. And then we could walk up to people and say things like, "If you spend 25 cents on nickle items, I'll let you have another 25 cents worth of nickle items for free!" and people would be ALL OVER that. Perceived value is a very strange phenomenon!