I don't think there is a "realistic" way to certify the existence of 50 thousand people online participating in a free contest. Every time, for every giveaway.
A good reference can be given by "real users" who actually "win" prizes, likewise people posting here on the forum from ranked accounts.
Regarding sports betting, providers carry out checks. this change it could be just simply from a review (or the system incorrectly) that provided one value rather than another...
Do you think all the participants are using this forum? If not then how the winner will be forum users? And if you mean known of forum users then I am at the same point that they might not be a known person of any reputed forum members. And why the site will take initiative while their are a lots of media?