The best sites will allow you to sign up and view your matches for free and will then charge a moderate subscription before you can communicate with any of its members. (eharmony.co.uk)
When viewing your matches you will see a percentage score given to each match. (arealkeeper.ie)
You can change your match settings to only view matches of a particular sex, orientation, location, ethnicity, height, age, etc.. (datingadviceguy.com)