When I wrote Digital Video Secrets, I decided that I would buy everything I wrote about. If I reviewed a camera, it would be one I personally owned.
As my books begin to sell and I gain credibility, I'm faced with the decision of whether to accept cameras from manufacturers on loan, and to then review them.
The advantage of accepting cameras on loan is that I get my hands on a wide range of equipment and do a better job writing about cameras.
The disadvantage is that I could conceivably write about a camera that I, myself, would not buy.
Lately, I'm favoring the idea of sticking with my original approach. Write only about cameras that I own.