Rented referrals on ptc sites!

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I have started using ptc sites about 2 weeks ago. i want to know what is the whole concept behind rented referrals. i have some questions- 1. do you have to pay for these referrals monthly? 2. how does autopay work? 3. do you have to pay any extra money?(for ex- on neobux you get 3 rented referrals at $0.66 so what i mean to ask is do you have to pay extra money apart from these $0.66) 4.how effective are these rented referrals? Thanks.