This would fall under automation and is not allowed by Blizzards TOS.

Auto-selling is a gray area for blizzard because the sole purpose is selling contents currently in your bag which you would do so anyway is not automation, just convenience of not having to click manually. Having conditions bound to auto-selling becomes botting as you are doing multiple things without interaction of the player (in your case crafting, and having the addon determine that it needs to sell those items which in term means it has to keep scanning your bags constantly).

You could of course just create a macro that closes the vendor, opens the vendor and put it on a loop on a button click, causing the auto selling to trigger but at that point you are already stretching what is allowed.