How can the gamblers verify that the actual amount of people are receiving the drop or the bonus, if there are no list to verify it? Let's discuss this.. I am curious if other people also thought about this... 
This is one of the problems that only blockchain transparency could solve, but as payments are made to internal addresses that only exist within exchanges, we will never know who actually won such a prize.
What could be done is for the casino to publicly disclose the nickname/login of the players who won, then we could know at least the fictitious names of the winners and if any of them said they didn't win the prize, then we would already have a red alert to start investigating .
Anyway, I prefer to believe in the honesty of the casinos that are more popular, because I've always reserved myself to bet on them and not on any casino that appears around here.
I believe that the casinos we have known for several months have a lot of reputation to uphold and should act honestly.