I heard on the news that some people are using price comparison apps to compete with Amazon. Here's how it works. Go to Walmart and look for sales, closeouts, and clearance items selling at rock bottom prices. Scan each product's bar code with a smartphone app that retrieves the best online price. If the product sells for more online, buy the product at Walmart. When you get back home, sign up on Amazon's site as a reseller and then post ads for what you bought. Sell the item for a marked-up price that is less than the best online price. People interviewed by the reporter claimed that they could sell things online at a 50% profit.
https://www.cnbc.com/2015/12/01/retail-price-comparison-apps-empower-shoppers.html