Sadly, there is no real guarantee regarding your privacy. A company will state its policy regarding how it will use your data, such as in what ways it will share it, but if you read the small print you will not find anything that guarantees that you are safe in assuming that your privacy is ensured. You will only learn what type of data the company collects and how it analyzes it, as well as where it might disclose it.
A typical privacy policy includes information about the types of data the company collects and how it analyzes, discloses and stores the data; it doesnt necessarily guarantee that your information will be kept private. Furthermore, companies can change their policy at any time - so what you initially agreed to may no longer be valid in the future.