Nostr web of trust is mostly just feeds I like versus feeds I don’t like. So it protects you from spam. But it’s not the same as an explicit “I trust you” let me sign your keys with my endorsement that others who know me will now trust you more. It’s softer, so I think in nostr there is additional room for an explicit statement of trust. Maybe a new kind which is just a signed event that says I explicitly trust this npub.? 

Also just a second idea I think a note kind of debt between npubs might be interesting. I haven’t worked out the details but maybe something like an event which can be shared privately to define terms and then both parties sign the event and when someone posts it, clients can retrieve the events that show a debt, from one npub to another. And when a debt is paid the “receipt” of the payment can be a new event that is posted so the client determines the debt existed and is now paid? The only debt enforcement mechanism would be your reputation on paying these debts. Anyways that could be another mechanism that users could use to determine who they engage with from a social / commerce perspective.