Escrow works as a middle-man between two or more parties as he is trusted with the things/funds/service and is allowed to hold everything until the buyer pays him for the deal and then he sends the things to him and releases the funds to the seller after deducting his fee...

To make a successful trade, it is necessary to watch out the value of Bitcoins all time if you are already in, there are even exchanges which allow margin trading where you can even short your positions to make money off sell positions...