How does @at work

[cosmopolite]

@at command is not considered as dual clienting.

When you use @at to your vending merchant. The game closes itself. The
merchant attaches to client side.(or at least that what i believe)
Therefore you can play other account or shut down computer and go to sleep.

Edit: You can not play other character in the same account that is autotrading.
If you have sub-accounts that for autotrading. You have to find some methods to transfer items and Zeny. Avoid dual clienting.