That's funny, I thought all old uniform was supposed to be handed back in when you got the new one?
This board is full of complaints re poor Security at various airports; selling complete or parts of uniform is irresponsible as it might be used by someone to gain access to an aircraft or airside at an airport. It shouldn't work at home base, but it could well work at an airport off the normal routes where they are unaware of the uniform change.
Not a good idea to sell uniform on the internet.