There are many reports, researches and articles about wash trading volume in cryptocurrency market. It is more seriously with modern trading which is supported by trading bots. Now people use bots to trade and manipulate the market.
Manipulation exists in all markets but with trading bots, it will help market makers to spend less time in front of the screen and still execute their manipulation plan very well. It does not only exist in this market.
They manually calculated the trading volume of BTC and compared it with BTC's trading volume of CMC, Coingecko, and other exchanges. These are some key points to their results of the report
Manually you can watch buy, sell orders and their changes to detect wash trading activities. However, if you want to prove it you must have bots to detect it and make calculations. It can not be achieved manually.