Their core issue, is, probably, that CMC provides ticker data - tells you the price, market, exchange and 24h volume. Some of their more advanced competitors like Coin.Market already provide live 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 fake price and volume data.