Improve Escrow system

[staddle]

One can use hashes as a proof that the item was received:
Scenario: A wants to sell an item, B wants to buy it.

1. A adds the item to the database, pays a deposit fee.
2. B buys the item with enough funds.
3. B sends a hash of a random number only known to B along with the funds
4. A sends the item to B using courier C
5. C gives the item only to B, if B gives C the random number that generates the hash saved along the funds
6. C marks the item as received, gives the number to the contract, thus proving that B has received the item and releasing the funds
7. A can withdraw their funds

Maybe also look into zero-knowledge proofs. Could be useful... zk-snark