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 you’re in the WordPress industry like I am (whether it be design, development, or SEO) I have accumulated quite the list of WordPress affiliate programs. I excluded those I found unsuccessful or pay too little to make a profit from, specifically ThemeForest, Creative Market, and low quality theme stores like Template Monster. Hosting pays well and I wrote a tutorial for SiteGround’s affiliate program and StudioPress themes which are my 2 highest paying affiliates. Those tutorials have tons of screenshots/social proof especially for SiteGround.
Affiliate marketing is often touted as a "get rich quick scheme" by shady sites offering pyramid schemes that promise quick cash for little effort. Make no mistake—successful affiliate marketers like Pat Flynn of Smart Passive Income put in a lot of effort toward building an audience and creating quality content that will bring in sustainable passive income. Expect to do a lot of legwork up front—but if you play your cards right, you can build a solid source of revenue over time.