I doubt eBay is brokering advertising deals between their sellers and other businesses, as they would have to benefit from it somehow, which would be difficult if there's an incentive for the seller to include other businesses marleting materials, and there are no stores on eBay for the business being advertised.
Technically sellers aren't even supposed to include their own marketing materials unless they are only advertising their eBay store (i.e. you're not supposed to include eg a flier advertising better prices on your own website).
I've bought from eBay sellers who have their own websites and have received marketing for other businesses in with my purchase from the website (that wine one is pretty common), so I assume the deal is between the two businesses.
