Hmm maybe its legal since I actually see some dump and dump group but I don't really know if they are successful for that doing, But also as you can see if their are more buy orders it can set the price to go up and dump if rampant sale will occur so I think some rich people do manipulation act to earn and I don't see anyone sue for that actions so I conclude that kind of act is legal since it hasn't disobeyed any law of certain ones.