Walmart isn't a platform (excluding Jet.com). They purchase goods (take on risk) prior to selling them. Amazon is a marketplace meaning the seller takes on all

Walmart isn't a platform (excluding Jet.com). They purchase goods (take on risk) prior to selling them. Amazon is a marketplace meaning the seller takes on all of the risk and pays Amazon for the privilege. Amazon then uses the data that marketplace generates to undercut the sellers with their private labels.