Negotiated Market

A flea market would be a negotiated market. The buyer and the seller work out the price on their own...there isn't a third party involved who oversees the sale.

The person in the booth selling weird medieval paraphernalia has a broadsword for sale for $500 that was allegedly used on the set of one of the Lord of the Ring movies. You think that's probably a load of hype, but the sword is cool, so you offer $400. Eventually, you settle on $450. A negotiated market.

Many stock markets are negotiated markets. The NASDAQ, for instance. Buyers post bids. Sellers post asks. The market provides a system for them to find each other, but doesn't intervene directly.

Meanwhile, the NYSE works on a different system. It operates as an open outcry auction. Stocks have market makers who facilitate transactions when liquidity is low...there's a third party involved between the buyer and the seller shepherding the transactions.