This could be a concern while the site has only operated for a short period. During that period, keep your wagers small. After the business is seen to be profitable, it becomes something of a golden goose, and this threat would be limited to rogue employees rather than the firm itself. Protecting against rogue employees could still be an interesting problem.

Admittedly, the concern we're discussing is one reason why I wouldn't mind if this firm charged a really small distribution percentage.