Correct me if I'm wrong, in order to complete the tasks and earned with this affiliate program, you and each user you've referred must complete an offer which is like this
"To complete this offer simply sign up to Betfair, deposit £10 and bet through the entire amount.
Cost: £10.00"
And I guess no one tried that so there's no one get the .25 btc of this site.
Yap, you are right. This is the hardest task to do, to get active referrals who want to risk their money is always hard. Actually people can refer themselves but I think it will not be worth enough to do. On other side, the rewards are not escrowed so there is a risk that we wont get paid after completing all the requirements.