Their core issue, I guess is that CMC provides ticker data, not trade data. Some of their more advanced competitors like Coin.Market already provide such data (trades data), so you can calculate how much volume was for 1 second, 1 minute, or 1 hour and so on - you can also check how many trades were to get, for example, btc/usd in a selected price range on all exchanges or on one exchange - that provides much better protection from such fake data for users.