Sites like Share-A-Sale and Amplifinity provide referral fees. Vendors set the referral fees they're willing to pay and for what services. When the transaction happens, you get paid by the company for introducing a new customer to them. uRefer also allows merchants to set up referral programs for introductions and meetings, in addition to any transactions made.
If my piece of content is so unique and valuable around hiking backpack recommendations, that other reputable outdoor websites are willing to link to it and build the page’s authority, then I’d have a very real opportunity to rank high in organic search for these search terms (meaning, my page will come up first when someone searches for hiking backpacks).