A good deal of your answer will depend upon the type of business that you have. Manufacturing businesses can be more complicated and will often require more "due diligence" from prospective buyers than businesses that are more service oriented, such as laundry mats and car wash businesses. These types of businesses will often have much simpler financial statements but they can also be tougher to value because they tend to have more "off the books" income.
In general, buyers will want to see copies of your at least the last three years of your business tax returns, as well as the current financial statements from your business. This would include annual income statements, a recent balance sheet, and a statement of cash flow. These can and should be prepared by your accountant. You will also want to prepare a detailed list of the assets that you are planning to sell. Before you allow anyone to review your tax returns or financial statements, I would strongly recommend speaking to a business law attorney in your area.