Is your feature request related to a problem? Please describe.
It is not really a problem but quite an inconvenience.

Describe the solution you'd like
At the moment, when I am trying to sell stacks of an item in smaller increments, I have to continuously select the same item to try and sell in stacks of 5 or 10.

In addition to the existing "Automatically select next item" option, I would like to see an option to "Automatically reselect current item" that would continue to select the current item when I am selling it in smaller stacks. And when that item is completely sold, only then would it continue to select the next item.

+1, this is quite annoying when you want to sell items in specific stacks. At least there should be an option in settings to select expected behavior

Why are you selling items in small stacks? The auction house (from 8.3 onwards) now lets users purchase part of a stack that's been posted, so posting 50 ore will let a buyer buy just 5 (or 1, 2, 3, ...).

Cool, didn't know about that!
But I still observe an issue with the armor of the same name (which cannot be stacked) being skipped to next item.

If you set the quantity in the settings for Selling: Gear/Pets to 0 it will post them all in one go (with the ability to purchase just one).

That may work, will try it, thanks!

Ok thank you! I did not know that as I have been away from the game for years :)