Just about any industry has a very wide array of products that can be sold as it relates to any niche. If you start promoting one product, but over time another product becomes the better option to promote, you can change at any time.
There’s no commitment to keep selling one product or another. Heck, sell them both if you want! Most of my sites make money using affiliate programs from multiple different services. Also notice that I have many sites in many different industries which helps to diversify my business even more.