I always wondered how does affiliate for such sites work? justwatch too has affiliate links to all streaming networks. Do they sign up for affiliates for every

I always wondered how does affiliate for such sites work? justwatch too has affiliate links to all streaming networks. Do they sign up for affiliates for every available streaming network (which isn't possible as many don't have a program) or is there a syndicate affiliate network for this? I am building an price aggregator for a category of products and its so hard to sign up for each of their affiliate individually and balance everyone's T&C.