So… why isn’t guild reputation account wide (shared by all characters within the same guild)?
With such a system the account wide reputation would work like this:
Character 1 in Guild A is the main character and was the first char to join any guild. The char have worked up to Exalted reputation with the guild.
Character 2 joins Guild A and should automatically gain Exalted reputation due to Character 1’s standing, or perhaps rather the reputation rank below Character 1’s rank.
Character 3 joins Guild B, and have to work up reputation from Neutral because the account have no other characters with reputation to Guild B.