All of them are spam. Mods may not have noticed it.
It's something new to me. Can't one ask a person to join as his/her referral and pay for the same? I thought as it is considered a job, it's allowed.
See BadBear's post I quoted above. It isn't allowed. It is solely for advertising and what they are paying is what they get from referral earning. If there is any additional payment other than from referral earning, it maybe allowed. Some referrals are allowed in tasks like these. For example, to track new registrations/traffic from forum, site owners may use referral.