I've been around marketing a long time, and I know the idea of getting someone on your list then offering them more of your own products and other peoples products. Of course this works.
But if you don't do this wisely, you are hurting yourself. If I buy your WSO I may like it and want to get updates and rarely might look at other related offers but if you assume that because I buy something from you it means I want daily emails from you promoting other products you are wrong.
Recently I unsubscribed from someone who I've purchased 2-3 WSO's from but the amount of email from them was crazy. I looked and in a LITTLE over 2 MONTHS I've received over 120 emails from them. They are successful and so it must be working for them but it must also be costing them a lot of long term relationships. At least it cost mine.
Add the amount of email from this one person to the emails from other WSO creators who also think I want to know about their best buddy's new offers almost everyday and I'm grateful I set up a junk email account just to use for WSO pruchases.