I have already created one service for digital items Zapit.live you can put any content behind lightning paywall like blog, pictures, videos, anything. User will only get the content when they pay the invoice.
Discussion
Honestly it could probably work well for physical items even without an escrow. Look at dark markets, how many people finalize early if they trust the vendor? And a lot of these would presumably be known identities dealing with much less sketchy stuff lol still obviously risky though