Reasons:
Half of them have shitty grammar (Charizard Vmax has the word "price" instead of "prize" in the Vmax rule, as well as the Black Charizard Vmax, Pikachu Mega Ampharos's Tag Cosplay rule says "OnlyFAN ART card. Don't be used in TCG game.").
Most of their numbers exceed the final number (The Rainbow Rare Eternatus Vmax is 192/189, Rainbow Rare Tapu Koko Vmax is 166/163, Black Charizard Vmax is just 43).
They all look blurry as shit compared to a REAL Vmax.
Most of them don't have an outline around the card.
so yea, be on the look out for any fake gold cards (I'm probably gonna sell mine at a garage sale)