Anything with a lower market cap is easier to manipulate. This is true too in the penny stock market. Enter with buy and sell limits and protect yourself. Otherwise sharks will be waiting to hose you.
Yeah, I was thinking exactly about a correlation to the penny stock market. People need to be a bit more concerned with where the pump is going though. A pump too strong will carry people away and when those whales pull out, everyone's stuck in a weird limbo with the price dropping. Honestly, I don't think people should really get into altcoin pump and dumps as well as penny stocks because there's no security for you and you can get carried away so quickly.
If we talk about those fluctuations in the price of cheaper coins, then the reality of manipulation in the market are huge, because that is because the coin is cheaper and it is thrown to the market by large holders of these coins. Of course with Bitcoin this does not happen, Although large whales always adjust the market, When they want to either earn or raise the price for Bitcoin.