Some trading platforms really abuse trading volume. This is mainly done by young exchanges that want to achieve an influx of users due to the high volume of trading. Maybe large and well-known sites, also engaged in similar earlier.
Old exchanges highly manipulated trading volume, not they are young exchanges because i saw that from almost 3-4 years in the crypto space. I have experienced about some exchanges those are huge daily trade volume according to coinmarketcap. I am talking about
https://exrates.me/ its showing 2 million trade volume but when i am go to sell my asset than see there are no enough buy bid for sell my coin just remember that its how much manipulation.
Most of exchanges that manipulated trading volume are exchanges that foster the population of bots.
The bots make the exchanges very crowd but it's just trading between bots.
And also, coinmarketcap is not an accurate source to see the trading volume, we should research the exchange itself to know the real volume