The NES has the largest reproduction market of any console.

The screw test

Genuine NES cartridges use a 3.8mm security bit screw ("gamebit"), which has a hollow, splined head. If you see standard Phillips screws, the cartridge has either been opened and reassembled with replacement screws, or it is a reproduction. This single check catches a large fraction of NES fakes because security bits and screws are an extra cost repro makers often skip.

Caveat: legitimate collectors do open carts to replace batteries or clean contacts, and some replace lost security screws with Phillips. Phillips screws mean "investigate further," not "confirmed fake."

Label tells

• Genuine NES labels are matte to semi-gloss, never mirror-glossy.
• The black text and Nintendo Seal of Quality should be crisp at 10x magnification. Fakes show pixelation, especially in the seal's fine lines and small text.
• Look at the spine/end label where present, and at the "NINTENDO" text. Font weight and letter spacing are commonly wrong on repros.
• Genuine labels are recessed flush into the shell. A label sitting on top of the recess, or overlapping its edges, is a repro.

Shell tells

• Genuine shells have "NINTENDO" and a part number molded into the interior plastic, plus a date code.
• Check the cartridge's rear for the molded ridges and the correct dust flap mechanism.
• Grey shell color varies with age and sun exposure, so color alone means little. Still, a shell that is uniformly bright new-plastic grey on a supposedly 35-year-old cart is worth a second look.

Board tells

Genuine NES PCBs carry board codes like NES-NROM-256, NES-SLROM, NES-TLROM, NES-MMC3, and so on, silkscreened on the board. The ROM chips carry Nintendo markings and part numbers matching the game.

Reproductions typically show:

• A generic board with no Nintendo code, or a code that doesn't match a documented mapper for that title
• Flash or EPROM chips (Macronix, SST, Winbond) instead of Nintendo mask ROMs
• A battery added to a game that has no save function, or a hand-soldered battery on a game that should have a spot-welded one
• A donor board from a common game (often Mario/Duck Hunt or a sports title) with a new ROM piggybacked or socketed

Most commonly faked NES titles

• Stadium Events
• Little Samson
• Flintstones: Surprise at Dinosaur Peak
• Panic Restaurant
• Bubble Bath Babes
• Hot Slots
• Peek-A-Boo Poker
• Cheetahmen II
• Bonk's Adventure
• Snow Brothers
• Kid Klown
• Bandai Golf

If you are buying any of these, assume it is fake until the board proves otherwise.