https://wow.gamepedia.com/The_Schools_of_Arcane_Magic_-_Illusion11/11/2018 02:04 AMPosted by FlarepulseA mage could mask or nullify the scent of something by using magic, right? The first thing that comes to mind is the small questline before the Culling of Stratholme dungeon where the scourge disguise plagued grain in order to get it into the city.
I don't recall how effective the disguises were, just that the adventurers were able to see through it easily enough and dispell it with a quest item provided by Chromie.
Though it only mentions invisibility and inaudibility, I'd imagine illusion magic covers all manner of deceptive spells. The plagued grain crates are even said to be under the effects of an illusion.
The last line of that source I linked mentions that divination spells can counteract illusions; I'd imagine this is why we were able to dispel the illusions easily. Being from the future, we knew the plagued grain had to be there somewhere. Going around poking every crate with divination magic would certainly unveil it. In my opinion, the fact that we only find a limited number of crates 'suspicious' is probably just for gameplay reasons, so that people aren't spending an hour running around dispelling every crate in the area.
A mage would be able to mask/nullify something's scent. Unless someone knew something was up and tried to use divination magic to break the spell, it'd likely be quite effective as well.