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 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) provided one value rather than another...