Nintendo games rarely go down in value and the Pokémon series is no exception. The Pokémon games on the Nintendo DS can still fetch high-prices on second-hand websites, which has led to an entire industry of bootleg cartridges being developed and sold on sites like eBay.
The fourth and fifth generations of Pokémon games appeared on the Nintendo DS. The mainline Nintendo DS entries in the series were Pokémon Diamond, Pearl, & Platinum, Pokémon HeartGold & SoulSilver, Pokémon Black & White, and Pokémon Black 2 & White 2. These entries make up some of the most critically acclaimed and financially successful games in the series.
The Nintendo DS is Nintendo's best-selling system (and is the second best-selling system of all time, behind the PlayStation 2). Despite the massive audience for the system, it can be hard to find cheap copies of the Pokémon games online. If you get lucky, you might be able to snag a game card on its own for a reasonable price, but boxed versions of games like Pokémon Platinum and Pokémon HeartGold & SoulSilver are way more expensive now than when they were at launch.
The level of demand has far exceeded the supply for Pokémon games on the Nintendo DS. As such, the gap in the market has been filled by reproduction cartridges, which can be purchased cheaply on eBay. These cartridges are advertised as working on everything from the base Nintendo DS model to the Nintendo 3DS, which is the telltale sign that you're dealing with a reproduction.
The Nintendo DS line of handhelds was dogged by piracy throughout its run, with hacking groups quickly working out how to bypass the security of the system. The scourge of the Nintendo DS was the flash cart, which let consumers insert a microSD card that could store roms and run them on the system. The reproduction cartridges work on the same principle as the flash carts. These bootleg cartridges work around the anti-piracy features of the DS/3DS line and should work like existing Pokémon carts. Problems can arise with the build of the cartridges, as they tend to be of an inferior build and can struggle to last when paired with portable systems.
The era of the DS has ended and it seems that Nintendo and second-hand sites aren't interested in preventing the sale of reproduction cartridges, which is why it's still possible to buy bootleg Pokémon games on sites like eBay. The Nintendo DS had some of the best Pokémon games of all time, which is the main reason why so many people cling to their original copies. The demand for these games is so strong that it has created a hole in the marketplace and fans need to be wary of what they're purchasing if they want to return to Johto, Sinnoh, or Unova.