Yard sales are awesome when they're done right. There's nothing I love more than getting something, whether for me or someone else, that I just know is so cheap that I feel like I'm robbing the people.
A few years back, I saw a yard sale where it looked like they had emptied the entire house onto the lawn. The people holding it were the adult children of the deceased owner. They didn't feel like dealing with it, so they were selling it all for nothing. There were so many killer things there, so we just started offering like $10 for a box of stuff, like books, antiques, whatever.
We spent $65 there, and sorted it all out when we got home. We hit the jackpot. One box was full of some German cutlery and dishes with Swastikas on them, which the owner had taken during WW2. We sold those to a local antiques dealer for $650. One of the books in the boxes was a first edition of A Christmas Carol. It was in rough shape, but we were still able to get $2,200 from a collector who wanted it for his mother.
Through various other things we sold from $20-$200 each, we ended up making over $4,000 over the course of a few months from stuff we bought for $65 at a yard sale.
Then of course, you have the down side of yard sales. You know the ones - the jackasses selling everything for 5% below retail , even though it's 20 years old, used, and needs work. My neighbor did this last weekend. They were selling a small coffee table for $50. At a yard sale. They had used it for 12 years, it had water stains from glasses not being sat on coasters, and it needed refinishing badly. His whole argument for the price was that it was Amish made, solid mahogany, and he paid $300 for it. Needless to say, it didn't sell. The next weekend, I convinced his wife to take off the tag and have people make an offer. The first lady that was interested offered $25, and they took it. I think the lady overpaid, but she liked it. I just don't get what's going through someone's head when they price all of their stuff for almost what they paid for it, then cry when they make no money.
When you do a yard sale, you gotta take the Walmart approach - sell it all for nothing. My dad's ex girlfriend used to have yard sales where she wouldn't price anything over $1, and she made a couple of hundred every time she had a sale.