Each user's CRC is unique. You decide whose CRC you are willing to accept by establishing a direct trust connection with them. Indirect trust, where you trust someone who in turn trusts another, allows you to transact with people you don't know personally, making the tokens implicitly fungible. Think of it like a chain of introductions: if your friend vouches for someone, you're more likely to trust them too.
It’s important to only establish trust connections with people you genuinely trust. Trusting someone untrustworthy means they may extract value from you and your network. Building a reliable trust network is essential for both yourself and the network.
How do trust networks work?
This article describes the mechanics of Trust network.