Determine if bargaining is appropriate. It's foolish not to at a Greek outdoor market. You've put the merchant in a position to make the first offer. If he comes down even two percent, there's nothing sacred about the price tag. Shop around, and find out what locals pay.
Prices can vary drastically among vendors at the same flea market, and even at the same stall.
Ask English-speaking local customers for the going rate. Determine what the item is worth to you. Many tourists think that if they can cut a price tag by 50 percent, they are doing great. So the merchant quadruples his prices and the tourist happily pays double the fair value. The best way to deal with crazy price tags is to ignore them.