When people trade physical items, they can see it so there is a good level of trust. However, with verifiable computing powered by zero-knowledge proofs (ZK), its different as people can't see it.

ZK-proofs are based on mathematical proofs and cryptography and are almost as good as absolute truth, and can also be verified. Hence, there is no need for trust. You can prove that something was done correctly without showing how it was done, and everyone can verify that proof for themselves.
 
The basis on which proofs can be efficiently traded is "trustless trading"; that is, on the basis that trust does not need to be established.
 
Berry beautiful morning.