So Bitwise researched this and presented to the SEC when they were applying for their Bitcoin ETF back in january.
They found out that over 90% of the bitcoin volumes are indeed faked & came up with a list of top 10 exchanges with actual volume.
They cited 'Blockchain Transparency Institute' for this research... but the story is messed up. There's no information on who these guys are & CoinDesk later found out that Bitwise was involved as a partner. Now Blockchain Transparency Institute cannot be reached but their coin market data is still reachable here: bti.live.
But the question remains as to who Blockchain Transparency Institute is? Their data somehow supported the Bitwise presentation to say that Binance & Bitfinex are one of the top 10 trusted exchanges with actual volume.
There's an article which covers this story in whole detail here:
https://cryptowhistle.com/fake-volumes-of-cryptocurrency-exchanges-the-not-so-transparent-blockchain-transparency-institute/
Whoever they are, they exposed all fake exchanges and how they are faking everything.
I am yet to see why role Coinmarketcap has, and how much money they are taking for this.
This is latest BTI report from September 2019
https://www.bti.live/bti-september-2019-wash-trade-report/
And one report from Cryptocompare website
https://www.cryptocompare.com/external/research/exchange-ranking/?social