If you have an eye for design and some experience of creating websites, then you could offer your services as a freelance web designer. You will need to create your own stylish website, and have a few other projects that you can show potential clients to demonstrate your skills. You will also need to initially spend time emailing businesses to promote your services and find work.
I personally prefer to do it that way--you can create a more convincing review that's more likely to make sales. It's not always possible or practical, though; for example, would you break up with your significant other just to test a product for getting your ex back? ;-) In cases like that, or if the product is expensive, it's usually best just to use the vendor's affiliate resources instead.
If my piece of content is so unique and valuable around hiking backpack recommendations, that other reputable outdoor websites are willing to link to it and build the page’s authority, then I’d have a very real opportunity to rank high in organic search for these search terms (meaning, my page will come up first when someone searches for hiking backpacks).