The same thing can happen with members who join your list. Before you send your message, always think about the long-term effects that message could have. If you're just trying to make a quick buck, and you're not promoting quality, it will come back to bite you in the end.
That means if you're an affiliate you should review the products that you're promoting to make sure they are high quality. Don't promote something just because there is a high commission for you! The same thing applies if you sell physical products. Make sure that everything you do and the products that you promote are in the best interest of those who have subscribed.