Earlier quoted context omitted.
Part of me wants to believe this comment is satire, but the better part of me knows this is HN, so conceivably someone would call the barrier to entry for competing with Amazon's retail unit "very low"
In a sense entering the market is easy -- sign up to Shopify, drop ship from China, etc. On the other hand, competing in the market is not easy. Maybe that's what he meant?
The comment I replied claimed Amazon didn’t have competition, to which I wanted to point out that the retail side of Amazon has a ton of competition. And single digit profit margins are pretty hard proof of competition, and/or low barrier to entry. Because again, people have a goal of earning money, and the only reason they would accept single digit margins is if others would take their business.