Not for sure, yet what may work. If you write on a niche market then discover the eBay stores of that niche market. Choose the high selling products from that store and insert those into the capsules. You can specify product and seller in the capsule. That ties the niche article of a niche market to a niche supplier for an impulse item offered for sale.
If you own the store then it makes it even nicer. Plus, you may create a relationship for the eBay seller and get leads what does sell and what promotions will occur. And, many eBay sellers sell on Amazon too. A marketing structure could be built. Add Etsy and other selling sites and kingdom could be built.