The Dangers of Sharing Characters - Don't do it.

My very strong recommendation is not to share characters or moa files - ever.

If you do then you run the risk of
1) Being banned if they miss behave as we can not tell who is who. The ban would affect all of your characters not just the shared one
2) Havign your character stolen. The other person can change your password and you have lost the character.
3) Having your items stolen. This includes items worn, in inventory, in bank and in clan hall.
4) Having you reputation destroyed by rude or inappropriate actions taken by the other player. Neither admin nor other players will know that someone else is using your character and as such you will carry the burden of their actions.

Do not share your characters.
Protect your moa files. Do not leave them lying around.
Make sure your characters have a password.
Never buy or sell a character for real $. Apart from being illegal (in the game) it is also subject to all the problems above.

It is not up to the admin to try and determine who is who and in most cases it just is not possible.

Don't do it and a stack of problems will be avoided.