You don’t need addons to cancel scan, this is not an addon problem.
It’s the LIFO system, last in first out. Most players don’t under stand this. The system has been place for over 5 years and most casual players don’t know how it works.
If your dedicated to selling something on the AH, your gonna have to monitor the system through out your game play.
I post on the AH, do a key with friends then recheck to see if my posts are on top afterwards. If they are no longer on top, I cancel them and repost. And I don’t use addons.
Undercutting doesn’t work either, someone posts over top and they win the sale.