as much as i know ,

Escrow act as a middleman between buyer and seller


BUYER ---> sends funds --->> ESCROW <<---- sends funds <----SELLER


BUYER  <<----- Exchange --- ESCROW --- Exchange ----->> SELLER


Escrow will charge a small fees for this.

you can find a complete list of members who provide escrow services here.
https://bitcointalk.org/index.php?topic=108716.0

hope it will helpfull