As someone who has been dealing in militaria for over 30 years, I would advise anyone considering purchasing military badges on ebay to exercise extreme caution. Concerning brevets, as well as the non-existent aircrew categories mentioned above, there are many apparently genuine brevets and wings on sale which are not what they purport to be. For example, a genuine WW2 period pair of RAF pilot's wings could fetch anything from £25 - £50, yet a modern tailor's copy can be bought wholesale for around £2. Many of these appear on ebay purporting to be originals, in fact I would go as far as saying that at least 50% of military badges offered on ebay are modern copies.
I would advise anyone wanting to buy genuine old wings or brevets to seek out a reliable dealer who is willing to give you a written guarantee that you are buying a genuine item. In the case of you buying a dud online, forget the idea that ebay might help you gain recompense - they are not interested. By the way, I'm not drumming up trade - I've got no wings or brevets for sale, the only one Ive got is still sewn onto my No 1!