Repro carts.

[marurun]

Mass-market and "pirate" repros can also be a problem because 5v parts are more expensive and harder to get these days than 3.3v parts. Level shifters can be added to adjust to make 3.3v parts work, but those cost money and add complexity as well. Some cheap repros don't account for that voltage problem and can eventually cause damage to a console and the cart, ultimately resulting in the failure of both.

[Reprise]

For me, repros are fine when they're OBVIOUSLY reproductions. It could be a game never released in English with a translation patch applied, it could be a ROMhack, it could be a rare game with a label that says "reproduction" on it somewhere or with a shell that's a different color from the original release or something. Those are all totally fine and I own a couple though mostly actually-licensed versions put out by companies like Retro-Bit, Limited Run, or Columbus Circle.

What I don't like is when I *think* I'm buying a legitimate copy of a game and then find out that it's a cheaply made bootleg. I've had that happen to me a few times and I definitely don't like it. The bootleggers are actively profiting off of games that are not their own and are usually so poorly made that they can risk damaging a console. I'd much rather just download the ROM myself and play it on a flash cart so I'm not funding some sketchy criminal organization in China or something. That kind of thing rubs me the wrong way.
But if anyone LIKES buying and playing those carts on purpose and don't try to foist them off on someone who doesn't know better, that's okay with me.

I agree with this. I'm fine with repros if they are clearly labelled as such and it's quite obvious they are repros. I own one repro cartridge and it's Final Fantasy III (VI) for the SNES. It's a PAL cart and it's a clearly labelled as a repro (not that anyone would mistake a PAL FF3 for a real cart). I also own some repro Dreamcast games that were cancelled and never released.

As for the fakes, they are really starting to annoy me. I never thought they were a huge issue until the last couple of years. We have a large chain in the UK called CEX that sells second hand video games. About 4 or 5 years ago they started stocking retro. At first it was really good, as they were really reasonably priced and a lot of their stock was in fairly good condition. They're also online as well as on the highstreet, so you can buy any product from any store in the country. But then after a couple of years, both the resellers/"collectors" (which drove up demand and prices) and the scammers twigged and descended on the stores. The scammers have been exploiting the fact that CEX aren't retro specialists and so have been trading in loads of fakes. Not just fake carts either, but also fake boxes and reprinted inlays etc. It's getting ridiculous.