I want to purchase a copy of Pokémon Heart Gold, but I have no idea what I am looking out for when it comes to ensuring it's a legitimate copy instead of a repro

so this is my legit copy of SS and that's least something to look for in the front. On the back there should be the usual "Nintendo" logo along with some coding such as one row with something like NTR-580 PAT POND then one more row of code like IDFRENT 396 (i put in random as example. hope it helps