I dont know how M2U works nowadays. Back then during HKCW hot time, I did tried to do something like this with my M2U nominee account. Even if you place to sell lower than the first buy price, the system automatically match the price to the first buy price. Its true for vice versa as well. Thats why I think those who keep on pushing the price up by one batang are those who buy/sell through broker on trading ground.