It happened to me several times already, one being recently: I sold/GC-traded an item I intended to keep and use as glamour.
Why is this, with our glamour system as it is, requiring the original item we want to glamour in our inventories, still not a thing to allow us to lock gear of our choice, so it can't be sold/traded in or won't even show up on the sell/turn in for GC menu?

I get this is entirely my own fault, not paying attention and just clicking through all my items on that list, but it would still be a much appreciated convenience feature.
Some gear pieces require extensive farming or a lot of gil to aquire, yet the game doesn't even give us a way to protect them from accidental selling.