I used to work for a company that aggregated referral systems. These large IT groups that service large e-comm sites, like Nordstom, Macys, Target, Old Navy are set in their ways and difficult to build on top of for three reasons 1) outdated and complicated systems, 2) Poor change management - breaking changes happen all the time with little or no notice 3) there is basically negligible technical support - assuming you are admitted to the provider platform..

Making a link that sits on top of the right provider is hard enough but it's doable, getting paid the right amount if someone buys something from your link is much more the intractable problem.