I suggest to have an additional requirements that only user that is active for a certain period of time in the forum can only participate on the review campaign because abusers can use dormant account coming from account sellers just to use it for review purposes. This is good to reward only those user that is really using the forum and not those abusers that just use the forum for the sake of participating in events that is exclusive here.
Using forum just for the sake of participating in events cant be called as abusers.
Abusers are those who take an advantage of the event by breaking the rules of the events for their own purpose (profit).
As long as users are not breaking any rule (regardless how active they are in this forum), they have the same chance to participate.
Requirement to have deposit and wager is better than requirement of being active in the forum for a period of time.
If I have to suggest to make it better to avoid abuse, set a minimum deposit and minimum wager in order to participate as for now the requirement is to have 1 deposit and 1 wager only without minimum amount.