Based on what you told us it was a ripoff. You paid for a snorkeling tour, not an afternoon in a pricey tourist trap.
Of course, there are always two sides to every story, but it doesn't seem likely to me that a regular cruiser who paid for a tour would make something like this up for no reason. There has to be truth behind the post.
I personally get very tired of people calling other people "drive-bys" - so what? I have gone to firums and posted complaints about certain companies - if you have a legitimate complaint that is why the web offers instant feedback, to keep companies that try to rip us off honest.