To me, this seems like a trojan horse. “Here use our platform to process all your transactions.” Amazon then will know prices, inventory, and hot selling items. Amazon could then in turn use this data to undercut the local merchant online.
Don’t think this will happen? It already does with current Amazon sellers. If you have a hot product and Amazon recognizes it, guess what happens? Amazon buys the product from the manufacture at a much lower rate, undercuts you (not paying fees) and pushes you out by having a lower price.
Want to skirt around the fees and offer the product lower on your site? You can’t as by contract the price on Amazon must be lower or equal to the price on your website.
This is not a theoretical idea, it is currently happening.