Purchase of a Business » used between the Seller of business and a potential Buyer of a business. Eventually, you would use a Business Purchase Agreement to complete the deal. Purchase of Real Estate » used between the Seller of real property and a potential Buyer of the real property. You would use a Real Estate Purchase Agreement to complete the deal. Purchase of General Property » used between the Seller of personal property, such as a car or jewelry, and a potential Buyer of the personal property. You would use a Personal Property Purchase Agreement to complete the deal. Other Transaction » used between parties to document a potential transaction, such as providing goods or services over a given period of time.
As with any professional correspondence, you don't want to seem too stiff or formal, like you're writing a letter from a Victorian template or a bad spam email asking someone to send money to a deposed prince overseas—but you also don't want to be too conversational. You're not in a dialogue yet, so it's important to treat this like a professional first interaction, and not like you're skipping several steps and asking to meet for coffee. The tone you're reaching for is, "You don't know me yet, but I'm interested in your company and want to tell you more about why."