Abstract: The influences of an increase in noise trading before and after bidding and the level of takeover activities on the possibility ofmarketmanipulation were analyzed with an incomplete game model to explore ifdropping bid should be allowed after a buyer has bid. The conclusion is that the unique equilibrium leads to a non-profitable manipulation, and social surplus is increased by the possibility of dropping bids, if the level of takeover activity is high; on the contrary, the unique equilibrium results in a profitable manipulation, and social surplus is decreased by the possibility of dropping bids, if the level of takeover activity is low.