If you are selling your business you should not divulge trade secrets and confidential business information without a signed confidentiality agreement. The theft of trade secrets is an increasingly litigated issue. In the business sale context this often happens when negotiations break down and the potential buyer decides they can start their own business. It is important for the confidentiality agreement to include the right to obtain an injunction, damages, and attorneys fees in the event of a breach.
The first step in selling your business is to protect yourself. I also recommend you contact a business lawyer before you enter into any agreements or provide trade secrets and confidential business information.