Well, to be honest, from a money standpoint, last month sucked compared to other months that we've had.
I am pretty sure this is due to 'people waiting for the new game' impacting the fun of the current setup.
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I think the percentage of purchases might be a good way to add a "bonus" to referrals... to get people to find referrals who will buy things.
I think 10% might be a bit much for us right now, plus we want to encourage people to find referrals anywhere, not just paying referrals, so I think a two-pronged approach might work best.
You get a flat finders fee in SD after a referral plays x amount of time or moves or whatever (to help prevent referral fraud).
You get a % bonus of the SD that they buy.
etc.
Though now that I think about it having a higher percentage of on the SD purchasing but no flat fee would work probably just as well. People would be encouraged to find as many referrals as possible in the hopes that their SD bonuses would go up, since not all referrals would purchase anything.
You also wouldn't have to worry about referral fraud since only paying referrals would count, and we're not giving away money out of nowhere.