Like most of crypto fan I use Coinmarketcap to check the current marketcap of cryptocurrencies.

Question : are theese Data reliable ? does they reflect the reality ?

As the price of a cryptocurrency rises or falls, its total value is usually measured as market capitalization. In the case of a cryptocurrency like bitcoin, the market capitalization is calculated as follows: the total number of coins issued, multiplied by their price.
But according to Julian Hosp - co-founder of the cryptocurrency TenX - this calculation has major flaws in determining the real value of a virtual currency.
In a commentary for CNBC on the risks facing the cryptocurrency market, Hosp explains its argument as follows: "If a cryptocurrency has a market capitalization of $ 1 billion, that doesn't mean that $ 1 billion has been put into that cryptocurrency," he said.
"So, for a cryptocurrency with a market capitalization of $ 1 billion, maybe only $ 50 million has been invested in it."
"Therefore, if this currency disappears completely, its market capitalization will go from $ 1 billion to zero, but investors will have lost only $ 50 million."

After a few research, I found an interesting website named "Messari" : they say they provides reliable data and market intelligence for crypto investors and professionals. On their website the traded volumes of the first 10 cryptos are totally different than the ones Coinmarketcap shows. For example :

BTC trade (Volume 24h) on Messari : $ 1,106,074,445
BTC trade (Volume 24h) on Coinmarketcap :$ 35,507,520,048

This shows us 2 things :

1) that the goal of a Bitcoin @ 1 Million USD is still far away.

2) that the cryptocurrency market is still easy to manipulate for people who own a lot of money.