Ask HN: Isn't the trust model in blockchain broken at the periphery?

I have been pondering about end-to-end trust in a blockchain based system. A crypto-currency blockchain has end-to-end trust as the value (crypto-currency in this case) is generated and consumed within the chain. There is no outside element. But a non-crypto-currency blockchain will rely on an external party pushing value/information/knowledge into the chain as a fact. Let's take real estate as an example. You would generate some kind of hash from the details of a property and puts that hash into blockchain in order to track it. But what stops a party from putting hash for a non-existent property in the first place? I may be missing something basic here but my head is going crazy as this is a very fundamental thing.