There are large number of trading sites are available on internet and you can make transactions with a trust like we can buy and sell coins from online exchanges and they have a good trust of the users on daily basis they do a millions of transactions and for their smooth operations trust is important and traders are good because in every situation they earn their commission for transaction.
I guess traders do not run for exchange because of its popularity i think what they look for exchange is the alternative coins they want. Not all exchange contains high potential coins that would be a contender on the market. Although trust is given and to be consider on an exchange the need of great coins is essential rather than just mere trading different coins. Where do traders hang out? i guess they are on high capitalized markets.