i am pretty sure and i believe that they can even scam people with "provably fair" system, as people seem to loose really huge amounts of money
Provably fair system doesnt prevent the operator / site to not cheat on your rolls but
it is making it harder for them to cheat because player can verify their own rolls if they feel there is something wrong going on . These two words are different and some people misunderstood it completely
As for the example, 999dice is a scam site that implement a provably fair mechanism as well but as you can see there are alot people that still playing there despite the site is rigged.
References on how 999dice cheat with their "provably fair mechanism" :
https://bitcointalk.org/index.php?topic=948965.0Most people just seem to not understand what it means by "provably fair" anyway .The fact is that most people even think that with a provably fair mechanism on the site, they wont be losing with an insane loss streak which is not true (references below).
btw i dont trust now at moneypot provably fair system anymore after getting 24 losing streak at plinkopot.
This is just one of the many example that people mostly think they cant lose with an insane loss streak if there is provably fair
Provably fair means site cannot change the outcome to make us loose.
This only applied if you take a note of the seed before you roll, otherwise it will be easy to tamper your bet result just like 999dice did