I write for a gun magazine once in awhile. I'm commissioned to write four articles right now, and did a couple last year. So I don't do this professionally, but I've done it more than your average gun nut.
First off, there are a lot of misconceptions in this thread.
The writer is paid by the editor. Each magazine and its policies are different.
Some magazines let their writers keep the samples. Other magazines require you to give the samples back, or pay for them if you decide to keep them. Some manufacturers require you to pay for the review item. Others send them out for free.
I've written for SWAT, and have sent back every item I've reviewed, except for the ones that I had already purchased myself. The ones that I purchased myself were off the shelf at a regular gun store, and not massaged by a manufacturer. Part of your agreement with SWAT is that you don't keep free product, because that will bias you.
As for never writing anything negative, you guys apparently haven't read anything I've written. I've been negative. I've pointed out every problem, and malfunction I've had. If something broke I wrote about it.
I've written about companies where I really like the people who run them, and they were great folks, and even then I've had to say negative things about their guns. I had one product that flat out broke during use, and I wrote that up. I also wrote up how they fixed it, like they would fix it for any regular customer.
If a gun doesn't work from the factory, of course we send it back. If that happens, I also note that I had to send it back. A 2,000 word article about a gun that doesn't shoot is kind of hard to write.
There are some magazines that are known for being a little more "enthusiastic" than others. (polite way of saying that they're whores). I know a couple writers who love every gun they've ever got for free.
Keep in mind that the writer is going from a sample size of one. So if you read a glowing review, it is possible that he is telling the truth, and his gun did run perfect. We see the same thing on threads here all of the time.