you got a link to the auction?
if youve advertised it as a rs turbo item then it isnt really
yes it would fit an rs but it could also fit an evo or and evo could fit a fiesta
i would have sold it as a ford accesory spoiler and said in the description excactly what you wrote in the email to them "the item is a genuine Ford RS part that was advertised in the 90's to fit the Ford RS fiesta, and the ford RS-TURBO fiesta, and was sold through official Ford dealerships. The item will also fit every single Ford fiesta MK3, including the Turbo models."