Thanks Jochem. Not sure if I got your question 100% right but I would argue that in many cases of p2p marketplaces the platform plays a very crucial role, not only for facilitation of the transaction but also for curation and trust (e.g. Airbnb). In general, I think it’s hard to distinguish between “platform” and “marketplace” since thosw two terms are often used for each other.
On another note, I think Bitcoin also fits to this peer-2-platform-2-peer model where the “platform” is actually the protocol and herby creating trust between the two parties.