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.
Coingecko did said some time ago they will put an end to fake volume reported by exchanges, i am still waiting how tha pawn out frimt coingecko end. As far as CMC is concern i don't think they have it in plan to stop fake volume by exchanges.