1. How do we know if a character is who they say they are?
IMHO, due to the decentralized and largely uncaring nature of the Third Imperium, I have developed this hasty generalization regarding Identity: Once you leave the starport,
you don't know. Not everyone amongst the trillions upon trillions of Imperial subjects needs an "Imperial ID" to start with.
A. If you have never been out of your home system:
* The Imperium does not know you and does not care who you are. You are, as always, subject to laws, rights and restrictions of your home system outside the starport. Your Identity as such will be established by whatever local tech level and standards the planet has. But "Imperial Entanglements"? Nope, not unless you use the starport directly or work in it directly.
B. If you leave, though:
* Military (Navy, Marines, Scouts, Army) will typically get some uniform identity validator. This allows for transfers and service record lookups when in the service and additionally for benefits when out (or detached duty for Scouts)
* Nobles who want to or need to travel away from home need some uniform identity validator so they are accorded the respect and benefits of their station from lessers.
* Personal Starship Owners would need Imperial ID so docking fees are charged in a timely manner.
Locally, oppressive governments may require ID and as Tech Level increases be able to use the same standards of whatever is an "Imperial ID" and access wholly owned Imperial Databases.