It isn't that hard to figure that out even if you don't have actual evidence. Logically, if you have enough coins to manipulate the market to your advatage, why won't you? And i think there have been several instances where a single transaction from the same wallet address bought or sold enough coins to move the market.
that's the point, there are too many person who have a lot of average of coin that can control in the market. They are rich from crypto and they become richer because of opportunity they have. I think there are some whales that composed of too many members that's why there are same address.