We know that even large exchanges constantly support the liquidity of cryptocurrencies, especially those that have small volumes. There are also bots that keep the price in range for the visibility of trade. All this creates the illusion of demand for some junk coins, and if you try to sell a large amount, the price will fly off to zero.
That is indeed true. Because I myself saw an exchange that uses bots to maintain the price of crypto currencies. But as long as it's good for crypto, I don't mind that. So it is necessary to avoid crypto which has a low volume in exchange.