why will they list that coin at the first place if that coin is fake or dont exist ? they inspect it first and they provide rules that those only the coins can enter on thier exchange .
for your second question , is that a volume your refering to ? even the top exchanges are also suspected before to have a fake volume on some of the coins that they list . i think exchangers them selves can monitor that easily . they dont lie because its not thier fault  but except maybe to the fake exchange  . shitcoins do have a value to so i dont consider them a coin that dont exist .