Exclusivity.
Most purchasers insist that you grant them a period of exclusivity before starting their due diligence investigations into your company. There are two reasons for this. Firstly, they want breathing space to complete the acquisition without worrying about competing bidders. Secondly, due diligence is an expensive exercise, regularly costing purchasers more than £250,000 in fees. This represents a significant risk for the purchaser, so in return it expects a commitment from the seller not to negotiate an alternative deal with rival acquirers.