We had 2 yard sales this season.  For the first one we had most of our stuff priced and it did make it easier.  People weren't constantly asking how much do you want for this.  For the second one we put out a sign that said "Everything $1 or less" and that worked really well too!  I think having the big sign out there got people to stop! 

I just did a yard sale last weekend.  I did price the items, though VERY cheap and then put out a large water jug with a sign asking people to help us reach our team goal.  I also bulk priced like "All Clothing $.10", the same with book, videos, shoes and so forth.  I only had two people try to negotiate the prices and my reply was "It's for the American Cancer Society"  I think that if you are not going to price items, be prepared for low offers.  As far as advertising goes, I contacted a local bank with a scrolling marquee located on a main intersection who put our event on it, the village paper did a nice write up on us as well and I was able to get into the calendar sections of two other papers by sending press releases.  Last year when I did the yard sale, no one came off of the add I placed in the paper, so this year I didn't place the add but soliciated the papers to just add my event to their community calendar sections since it benefits the ACS, and most were very accomidating.  I hope that this helps out.  GOOD LUCK