If you take the company's name from the certificate for a free cruise and put it in a google or yahoo search with quote marks around it I'm sure you would see a bunch of complaints. They get you money then sudden the date isn't available the deposit is much more then "real" port fees should be. My hubby and I got one of these once. I researched it then put the certificate in the circular file.
The one I got was for a Carnival Cruise in a 1A cabin the "port fee" were about $250 for a 4 day cruise.