While I'm all for saving money and that, I couldn't possibly see myself handing hundreds, if not thousands of dollars to somebody I know nothing about other then they responded to a e-mail of me requesting a cruise fee.
I'm spoiled though, I have an agency I've been using for 16 years now, and every time I go to book I always compare prices, and they are usually pretty close to anything else I find, certainly not significant enough of a difference for me to switch.
I may be in the minority, but to me, it's just too big of a purchase for me to do thorugh somebody I know absolutly nothing about.
I would suggest you also look at going directly with the cruise lines, or seeing is you could get recomendations on a local cruise specalist and seeing how they compare.