Provably fair is usually only as strong as the reputation and trustworthiness of the casino. Dice isn't as vulnerable to the attack you mentioned as users can roll over/under and use unpredictable multipliers but you still raise a valid concern, any website can recognize a pattern and plant a seed that makes the player more likely to lose. That's why it's important to set your own custom seed and when re-randomizing you should write in your own seed rather than let the website hand one to you.

Witty