One way is to look at their verified public key https://twitter.com/i/web/status/1603945963944480768 through the Nostr Directory https://www.nostr.directory/ and check to see if it is legitimate.

1) Users that you follow should be displayed differently

2) Users that are followed by many people you follow should be shown differently

3) When you follow someone, their name at the time should be saved to your contact list. If they change their name later, it should be shown differently. (Or if many people you follow know them by a different name.)