For me personally, this is a major deal breaker. I just finished Pokémon Y, and started playing Ultra Moon. All was fine until someone offered me a hacked shiny Haunter Lv.28 (evolved to Gengar), made to look legit, with perfect IV’s/ EV’s (hatched in the same day, lol), holding the mega stone.
I did some research on the subject. Downloaded PKHex and even transferred my Pokémons from Y to Ultra Moon, something i could’ve achieved via legal means (eg. Poké Bank). Which is okay, i suppose. Only i just started the game, if you know what i mean.
To cut to the chase, if there’s no way to tell whether a Pokémon is hacked or not, provided it’s properly done, why should i ever bother to trade or battle again? If i wanted to battle on those terms i would use Smogon, which offers a pre-built environment suited for competitive battle.
Why stop there, why should i waste my time catching, leveling and breeding Pokémon if other people can do it effortlessly and there’s no way to separate the legit guys from the hack players? I’m considering stopping playing altogether, or at the very least abstaining from LAN interaction until i beat the story mode.