if you want to be online selling then put your setting to the lowest and then log in and sell your item.
Why do people always assume the OP wants some hidden agenda.
Read literally, don't assume or accuse. People already do AFK bazaar. Streets are already cluttered. And there is no way it can stopped from happening.

Since you can't avoid clutter, only solution is to alleviate the clutter. One solution is by allowing players to use retainers else where that isn't as cluttered. If additional regulations are applied to where you can place it, it should distribute the bazaar evenly. Yes, this possibly could end up as more characters models spread across the world, however it is less likely that they are all clustered in a small such as how it is at Ul'dah right now.

As a side effect this would also alleviate the Market Wards clutter since you have to decide where to place your retainer.

Again, for the third time.
You can not avoid player clutter.
You can not avoid Market Wards overpopulation