Then if they only create poor outcomes for you each time, you will quickly see it and notice that the true RTP of the game is way lower than the expected one.
It could be done in a way that was basically impossible to prove, and even if you did suspect something and were correct, I would expect you would be treated similar to the way the all too frequent 'I lost too much, it's rigged, you scam site!' player is treated.
They could easily decide to make it impossible for half the Royal Flushes and half the four of a kinds to be dealt and that would change the house edge of their jacks or better game from ~1% to ~4.5%
It would take hundreds of thousands of hands to have evidence of anything suspicious and millions to make a confident accusation.
Just added 28 more casinos to the list.
Well I think with only "few" thousands of hands, you can already quite "confidently" check if the House Edge is of 1% or 4.5x times (4.5%) bigger than that in reality. But I agree with you it could be more transparent and trustworthy than that, if they would use an algorithm allowing a client seed for the randomization of the deck or an algorithm using an external and transparent source for the the randomization process as suggested by Danydee.