Here's a quick tip for handling money as you shop yard sales. Keep your coins separate from your cash. A change purse with hoarded quarters is ideal. You don't want to approach a seller and ask for a better price with a twenty peeking from your wallet! Somehow I always get better prices when I am counting out change, instead.
How do you bargain without seeming rude? I always smile, ask "Is this your best price?" and wait expectantly. At least half of the sellers are unsure of pricing and easily agree to a lower amount. I am very shy--so if I can bargain, you can, too!