There are many exchanges that are faking volume. Some reports show that there is up to 90% wrong volume reports. With market developing i am sure there will be more strict rules and penalties.
I think this is the next step in crypto for further development.
There should be some index be issued based on volume to track real volume of top 10 or top 20 exchanges who should be then monitored by some external company.
I hope also CoinMaketCap will take this issue into consideration soon enough to get some real data on smaller exchanges as well.
Those people who have long been trading in the crypto market are well aware of those exchanges that engage in deceiving users and artificially increase trading volumes. I have long ignored such exchanges and trade only on those exchanges where trading volumes are shown almost without cheating.