A Senior center in a neighboring community does this with great success. I'd like to see a "Make an offer sign". That would make me feel more comfortable right away at someone's yard sale.Next step is taking items that don't sell and boxing them with more sellable items, and make the box affordable. That way you get rid of the trinkets for them to worry about.
Same with charity stores, you don't try and donate individual items, you donate by the box full and let them sort it.