Bill values his privacy.
He likes to sit at home in front of his computer and write (more) books to help and entertain people. It really tics him off when the phone rings and somebody wants to sell him something he never asked for, and it really tics him off when his in box is full of offers from Nigerian princes, for Viagra and Prozac without a prescription, or penis- or breast-enlarging spam.
Therefore Bill has made a pledge. He will never use your email or contact information for any other purpose than to make sure you get the product you ordered, to let you know about current or future offers or the newsletter you requested, and he promises to be low key about that too. Furthermore, he promises he won't call you in the middle of dinner to get you to switch long distance carriers.
So because Bill values his privacy, he values yours as well.
Bill is a reasonable guy and if you let him know within a reasonable amount of time (2 weeks) after you buy something from him that you are dissatisfied with it, he will refund your purchase price (less any handling fees, which are usually minimal). Sound okay?