Seller stated it was untested and may or may not work in the listing, which I presume you read before clicking buy, and you must have thought it was worth a shot.
So whilst you could pursue it, and will probably win because they put it in the wrong category, IMO you should chalk it up to experience and leave the seller alone. It was your mistake.
Item was listed as used.
How much did you purchase it for? If it is a little then just learn and move on if not maybe worth opening a case because it was listed as used rather than for parts or not working.