I've read suggestions about creating your own 'product' to sell or give away to build a list, but is a product always some sort of ebook? If you chose a product to sell, such as a baby's toy, what kind of product could you create that's relevant to the toy? Sure you could write an ebook on child safety or baby development, but no one would buy it as they're just interested in buying the toy.
What if you created a niche website about winning back your ex or something else very specific? Surely you can't create a relevant product for every niche and know that it will sell?