Imagine a wishlist or collection, and you can tag things as 'sealed' or 'unsealed' - and then filter your collection / wishlist by those tags - tags can be anything a user wants and are unique to that user. They would be shared across a collection and wishlist so you wouldn't have to enter the same tag twice. Wishlist tag ideas could be reatiler - so tag a bunch a decks with 'ebay' if you know you can find them there, etc...