Sometime it can be manipulated, and most of whales are manipulating the cryptocurrency by the price, but we should to be aware and should be stronger in take decision because it can be a trap for us before buy or sell any coins.
It will not work for the whales of we will be determined and not to sell, they just do this for their own betterment, most of time new users get trapped by them but those who knows will never sell their bitcoin to help them manipulate the market, actually they do this pre planned for better low price bitcoin, they sell high amount of bitcoin in market so price gets down for higher supply them those greedy and clever whales buy double amount of bitcoin to increase their income.