When I was a kid it was my premier way to get bulk fake Pokémon and Yu-Gi-Oh! cards. What was crazy to me at the time is they were properly sealed in packs. Very obviously fake though. Thick, waxy, overly saturated with very low res and wrong fonts. Not to mention at least 4 years old. On the Pokémon cards the text and overall look was right though, so I still used them on the playground.

The Yu-Gi-Oh! cards, however, were the extremely fun poorly translated ones. “Spell Slame”, “GGGG”, “Rock Corrosion Devil - Love Fake”. I think my favorite though was a “Storm King” I traded for a legit Blue-Eyes Ultimate Dragon. I told the kid like 3 times it was fake, but he was bound and determined. Worked out for me, since I ran Blue-Eyes, but was just very weird.

Where I live, there are flea markets that banned all commercial reseller types. With time, those with the bans in place obsoleted all others without them. The people have spoken. If you'd like a proper flea market with lots of private sellers trying to get rid of miscellanious stuff from their basements, I recommend to suggest such a ban to the organizers in your area.