The flea market in a dream often symbolizes a meeting place where you can find items that may not be available in your locality. If you are selling something, it could also signify the end of your business.
If you are buying at a flea market, it may signify that you are looking for an affordable solution to your problem, which is not available in the current market.
If you dream about buying at a flea market but cannot find anything to buy, this signifies lack of confidence and being too shy to take decisions on purchasing something which is new or different from what is already present in the household.
A few flea markets occur in dreams as nightmares when they represent loss or difficulties with money and finances.