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.
Affiliate marketing owes its birth and first developments to CDNow.com and Amazon.com. Back in November, 1994 CDNow started its Buyweb Program — the first online marketing program of its kind at that time. Amazon continued this pattern in July 1996 with its Associates Program. Amazon claims that currently the number of their affiliates worldwide exceeds 1 million associates. (A Practical Guide to Affiliate Marketing, p. 11)
There are two ways to approach affiliate marketing: You can offer an affiliate program to others or you can sign up to be another business's affiliate. As the business driving an affiliate program, you'll pay your affiliates a commission fee for every lead or sale they drive to your website. Your main goal should be to find affiliates who'll reach untapped markets. For example, a company with an e-zine may make a good affiliate because its subscribers are hungry for resources. So introducing your offer through a "trusted" company can grab the attention of prospects you might not have otherwise reached.