Accept that bargain Tiffany does not exist, no matter how much we would like it to. Tiffany never runs sales or places items on clearance. Avoid anyone claiming to sell new Tiffany merchandise as a wholesaler or distributor. The only place to buy new Tiffany & Co. merchandise is directly from Tiffany & Co.
Check the piece for the proper markings. Every single piece of Tiffany jewelry is stamped somewhere with either "Tiffany & Co." or "T & Co." It is also common for genuine Tiffany pieces have a mark with the trademark date, company logo and metal content, but not every piece contains this additional information. When a necklace contains both a chain and a pendant, both pieces will bear the Tiffany & Co. stamp.
Examine the links of the necklace closely. Genuine Tiffany links are always soldered together -- they are never pinched closed. The soldering on Tiffany jewelry is neat and clean. You should have to look very closely to see it.
Notice the weight of the jewelry. Tiffany uses only high quality metals, so the piece should feel heavy and solid when you hold it. If it feels or looks cheap, it isn't Tiffany.
Look at the lobster. Tiffany uses high quality lobster claw clasps. On silver pieces, the lobster claw should bear a "925" stamp at its base. If the stamp appears anywhere else, or if the clasp shows poor workmanship, the piece is a fake.
Inspect any lettering found on the piece. The lettering on a genuine Tiffany necklace will be sharp, clear, thin and look dark. Lettering that looks white or was done in a wide font are sure signs of a fake.
Read the care card, if it is included with the piece. Care cards say "Tiffany & Co." and nothing else on the front. Any care instructions will be centered on the back of the card. A card that has anything on the front other than "Tiffany & Co." or that has left justified care instructions is a fake.
Get a second opinion. In a matter of minutes, a jeweler should be able to tell you if a necklace is genuine or not.