To my knowlegde, i believe the best way to ascertain a fake volume, is by logging in to the exchange, and checking the trade volume on the exchange, after you have done that, you can then check the existing or available buy orders; if it can indeed be up to the volume stated by the exchange or coinmarketcap.
I do this because, there are several tokens with 10,000$ + daily volume, with buy orders of less than 500$
Even with this, always do your own research