It would be great to introduce a quality of life feature to indicate what clothing we have already collected and obtained when viewing merchant clothing options to avoid duplicate purchases.
It's already the case 
There is a tab which will display only clothes you don't already have in your wardrobe (I assume this tab is named "Not In Wardrobe" in english).
There is a tab which will display only clothes you don't already have in your wardrobe (I assume this tab is named "Not In Wardrobe" in english).
Never noticed before, will check that out later. That'll help lighten the load.