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.
When promoting a product, you are also promoting the person or organization that owns the product. This should be the first thing to know before selecting the product you are promoting. You surely don’t want your clients to be unhappy after purchasing the product. Trust me; they will never come back to your site again to purchase anything! This is because you have dented your credibility. Normally, any company or website with good customer service is bound to have happy customers.
You can sell affiliate stuff if you did not use the stuff but a high, high, high, really high level of clarity is required to do this. Most bloggers lack this clarity. I recall Tony Robbins selling/being an affiliate for a $25K coaching class. Never took it. Never sat in it. But the guy made millions. He had full clarity in selling without seeing. So he rocked out the selling.
Can you make money with affiliate marketing? The short answer is yes, affiliate programs can earn a extra money and even a full-time income from home. The long answer is a little more complicated. Like any home income venture, success comes not so much from what you choose to do to make money, but whether or not you do what needs to be done correctly and consistently.