What if someone opens a brand new account just for this, in fact they could open 10 accounts at the same time, let them mature, and use them one by one until they reach 7 wins and then move to next one? And start a new one when the old one finishes, that way they would always have 10 accounts to use whenever needed. Abuse is always there, it is very hard to not get abused as a casino, it would be very tough for them to not get abused.
In order to do that, pre-arranged stuff won't work, they have to be manually checking every single winner and make sure that they are not cheaters, otherwise they would be pretty upset when they find out what happened.
I don't think the Betfury team checks each user manually. Betfury probably has a special algorithm that analyzes the behavior on the site, cookies, and user IP addresses. It seems to me this should be enough to successfully detect abusers using multiple accounts. In addition, the rules of the Funfury competition indicate that if Betfury detects multi-accounting abuse, they can seize the winnings from the abuser's balance.