Tiffany is one of the most faked labels on the internet. Not only is it well faked, but many of the counterfeits are made of sterling. The cost of Tiffany isn’t in the precious metal, it’s in the name so IMO you must put $7.50 into a professional authentication. Assuming it comes back as genuine, IMO you’ll easily get your $7.50 back in a higher price for an authenticated piece.
If you go this route and the ring is genuine, you can state that the piece was authenticated in your listing, name the company (but not in the title) and tell prospective buyers to email the company to confirm that they have authenticated the piece.