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Still they are doing it for money by investing their time rather than money as their capital.Affiliate marketing is kind of smart marketing strategies because they are not going to pay anything from their pockets they are only giving small part from the total profits.If there is no profit for the house the marketer also will not get anything.Agree that time is important but when we don't have money we have to find an alternative source which is the time.

That 'something more' is the time that they are spending for marketing their own affiliate links. There's not much investment from the management itself if these affiliate marketers are doing their job as you've explained zhekinsp with the share they give to them.
It's the most valuable thing for them and the more affiliates they have, the higher commission they get so it's up on how they market it on their own.