If you're buying:
1. Dress down
New York garage-sale aficionado Bruce Littlefield, author of Garage Sale America, says if you want to get the best prices at a yard sale, don't step out in your Sunday best.
"Don't wear expensive shoes," he says. "Sellers often judge how much you'll pay by the clothes you're wearing."
If you look like you have a lot of disposable income, you'll have less luck bargaining, he says. So if you happen to drive a fancy car, park it down the block and walk up to the sale.
2. Build a relationship with the seller
"A good sense of humour goes a long way. If you've made friends with the person that's selling, you're going to make the best deal," Mr. Littlefield says.
Being friendly isn't difficult, he adds. It's as simple as mentioning that the fine china the seller has on a table brings back fond memories of the kind your grandmother had.
3. Ask for a group price
Haggling over 10 individual items will frustrate the seller, so if you want to buy multiple things at a sale, buy them as a group, Mr. Littlefield recommends.
"If you say, 'Can I start a little pile over here?' They'll say, 'Oh, we have a buyer here.' Then say, 'How much for all this?' You're guaranteed to get a better deal going out of the gate that way."
If the seller quotes you $50 but you only want to spend $30, start moving things from your pile back to the table.
"I will tell you that it works every time. As soon as you start putting things back, they're going to make a deal quick," he says.
If you're selling:
1. Use the dime on a dollar rule
Don't forget that your things are used when you price them - it's just tacky to ask retail value for them, Mr. Littlefield says.
"If it's something you paid $100 for and you used it for five years, it's probably worth $10," he says.
You can tell something's overpriced if 15 people look at it but nobody buys it, so adjust accordingly.
2. Save the good stuff for eBay
If you have to defend an item's price with a long story about how it's a valuable artifact from the 17th century, you shouldn't be selling it at a garage sale.
"If that's the case, let an auction house take care of it or sell it on eBay," Mr. Littlefield says. "If something's a cherished family heirloom, you don't want to be selling it on your lawn and letting it go for nothing."
3. Be careful with price stickers
Use easy-peel stickers or tape to label prices, or just put a sign on a table - you don't want to damage the product. That big, black "50 cents" you've scrawled on a book with a permanent marker could kill a potential sale.
Mr. Littlefield says he's turned down many vintage board games he's found at garage sales all because the box was damaged by a too-sticky piece of tape.
*And don't do this:
Stop at a sale before driving by first; if you see people leaving empty-handed, it's probably a dud.