Heh, those can be rigged too...
One of those minesweeper type sites, I sat there for 20 hours playing it in "freeplay" mode... hiiiiiiiiighly successfully, had a winning strategy, well seemed to stumble on it in 10 mins and spent the other 19:50 testing, honing, refining, retesting ...
Yah, you can guess what happened when actual BTC went in.
Not much, but it will probably seem like it in 10 years.
Bovada does the same bait-and-switch type method with their casino games. I would play roulette or craps and win a hefty profit. As soon as I switched to real money mode, I couldn't win another dime.
Would need some proof that behind the scenes shenanigans weren't going on