Virginia transaction attorney shares how to write an effective and legally binding business purchase agreement. Sell Agreement (BSA) is a lifetime contract providing for the transfer of a business interest upon the occurrence of one or more triggering events.Under Virginia's economic nexus law, having a physical presence in Virginia is not a prerequisite for having to collect Virginia sales and use tax. Whether you are buying or selling a business, it is important to have an experienced business attorney involved as early as possible in the process. As a buyer, you need to know the terms of existing contracts and which contracts you will be responsible for fulfilling once the business sale is complete.