Manipulation only really works when the trading volume of a coin is low - that way you only need a little money to move the price.
Once the trading volume for a given coin is huge, it's hard to manipulate because you need loads of money to do it.
So the answer is build your community, make sure your coin is popular which results in large trading volumes for it - and the manipulation diminishes.
in this cases, of course there are people who are harmed because of that. and then , they claimed altcoins just a piece of scam.
whales alliance create a quick pump, then after they see many people got baited, they sold all their coins then price back to normal.
for example , we can see binance have a dialy pump with low volume trading.
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in altcoins world, there a many many coins/tokens created,also for god sake,too many exchange rather than coins/tokens.
hard to avoid manipulation or something like that.
i dont think it can be stopped,well ,its a free market.