Funny concept but I think you need to work on your site, and maybe get a free mode of the game, for users to test it out.
Also there are no examples on the ridles we will find etc. Maybe having a section with solved riddles, along with the free mode would help.
Finally how do you guarantee that the game is fair?
Click on the winners list. there is a demo that is the free version. Yesterday a user from here already won. There is no 100% way to guarantee it because its lottery but why not try it for 50 cents? Its not like your investing 10,20, or even 50$.