What do I do when I go to court? Do I have to pay the remaining balance?

If the jeweler induced you to buy the ring through false representations as to its quality, it committed fraud.  You would have the option to either rescind the contract (i.e. to return the ring and get your money back) or for damages (the difference between what you paid and the fair market value of the actual ring).  Although the ad may have been taken down from the website, you may be able to get a copy of it through the discovery process.  There are also some websites which store archived copies of other websites, and you may be able to get a copy off of one of those. You should carefully look at your sales contract with the jeweler, however.  It is likely to contain a "merger clause", i.e. a provision which states that the written contract is the entire agreement between you and supercedes any prior representations, oral or written.  Another clause likely to be found is one stating that neither party relied in any way on any representation not found in the agreement.  Such a provision could prevent you from claiming that you relied on the ad when you purchased the ring.