All of this talk and purple are ignoring the very fundamental aspect of this sort of transaction: trust.

When you buy from a place, you do it because you trust the store or the service to handle problems [1]. I remember one saying that a purchase is actually a very intimate relationship, and if you have any reason to think that person or service would screw up over, you’d never engage in any monetary transactions with them.

A marketplace where anyone can sell only works because despite your diligence to look for reputable sellers, the platform usually offers some assurance that you’ll be refunded for any type of scam, which means they take on the burden of doing some quality control on approving sellers. At least that’s how it works in Brazil, I suppose that a country with a high societal trust might have less of this problem, but the incentives are the heart of any system.

[1] Sure, sometimes it doesn’t go the way you wanted it and you can end up being screwed by the service, but the expectation was there.