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.
Mistake #2: Using the “They must not be my people” excuse to be spammy. I’m not a fan of this common tactic. Here’s how it works: people send a huge number of sales/promotional emails to their list with no warning and with no easy way to opt out. When people complain or unsubscribe, they put it on them (“Oh well, they aren’t my type of subscriber anyway…”), instead of taking responsibility for the spam (let’s call it what it is). What ever happened to “treat others the way you want to be treated”?
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).