Don’t only over-deliver when you sell a product for money, you can also do it when you promote something that is free.
When you promise something in return for an email address, don’t just deliver what you promised, add a surprise bonus. Selling and delivering the free stuff need the same attention as paid items.
People resent paying for shipping, especially for low priced items.
Have a bundle package for many of your products, so when they pick one of your products in your e-commerce store, show them that if they buy the bundled package (more of the same item, related items, etc.), they’ll get free shipping.
Have a better audience for your website.
A website that shows no content unless you are logged in as a member. Membership is free, but you have to register. No functionality or content are given without registration. It’s a secret “club” for members only.