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You don't need to go out of your way to look ratty, but avoid obviously expensive clothing. Chances are you'll be negotiating over cheap items, and a fancy suit or dress tells the seller you can afford to pay full price. Don't forget to remove flashy jewelry and watches for the same reason. In the last hour or two before they pack up and leave, sellers will be eager to get rid of their remaining merchandise   The flip side of arriving late is a smaller selection. For maximum choice (but higher prices), arrive early. If the flea market is seasonal, the time of year can also have an effect on the price. When the flea market has just opened, sellers will have a large inventory from the off-season and may be eager to offload it so they have room to obtain more desirable goods. Once you've found your item, decide to yourself what you're willing to pay for it. Having a clear boundary will prevent you from being convinced to pay more than you are willing.  Never reveal this price to the seller! If you do, he has no reason to offer you a lower one. You can try browsing around first to get an idea for how similar items are selling, but there's no guarantee you'll find anything comparable, and the item may be snatched up in the meantime. Most vendors expect haggling, but offering less than 50% the asking price will only offend them. Asking for a 25 to 50% discount is usually considered reasonable as an initial counteroffer at a flea market, although the final price will more likely be 10-25% below the listed one. Saying "hmmm" or simply pausing before you reply will make you seem less willing to purchase the item. This gives you more bargaining power.  Simply remaining silent can cause them to respond with a better offer. This works better if you have the seller's full attention. If you're trying to buy a $1 keychain, the seller might just ignore you and move on to another customer! After a pause, respond with a new offer between your last one and the seller's current offer. Continue to show hesitation until the seller reduces the price below your secret "maximum price". If the seller won't reduce the price to that amount, try these other tactics:  Agree to their last offer on the condition they throw in another item you're interested in for a reduced rate.  Have a friend pretend to pull you away or convince you to move on. This may trigger a final offer from the seller.  If you don't have a friend handy, simply start walking away for the same effect. Once you try this, though, you won't get a better deal if you walk right back to the stall! Pull out the amount of cash you're offering and show it to the seller to tempt them directly. Don't try this with a large amount of money, or anywhere with a high risk of pickpocketing or mugging.
Dress down. Arrive at the end of the day. Secretly decide on a maximum price. Make a low but reasonable offer. Show hesitation before responding to their counteroffer. Continue negotiating until you agree on a price or the seller balks.