Offer what you think is fair, keeping in mind that at the beginning of the yard sale the seller's objective is to sell as much as possible at the best price without giving stuff away, Papsin says. Never make an insulting offer.
"However, cash is more valuable to the seller than the item," he says. "If the price marked is $50, offer $30 and then hopefully you'll reach an agreement somewhere in the middle. Just use common sense."
If an agreement can't be reached, ask if there will be any 'last-minute incentives' like half off during the final hour of the sale. Or, ask if you can renegotiate on that particular item after the sale is over.