It isn't about if their integrity is actually compromised. It's about the suspicion that it could be. If personal intentions were as easy to read as the public ones, it wouldn't be an issue, but sadly that isn't the case.
Yes, that is the main issue but as I said, the quality of your work should prove that otherwise.
A good analogy is in sports. In my city, the game organizers shower the local journalists with free food (exclusively, mind you; if it were for everyone including the public, no one would care, right?). Local media outlets can be seen as ethically imbalanced for accepting any special treatment because it affects their coverage of the game and their opinions of the vendor. Instead, they'll give those vendors a lump sum of money (like I mentioned before) that avoids that problem all together.
I don't think sports is a good analogy for this. Local media outlets for sports cannot spin bad performance or a bad outing like what a bad game journalist does. At best, they can provide color commentary which local fans can enjoy. Coverage for sports is not as subjective as games as there are officials/committee upholding the rules for sports while games are entirely subjective.
In journalism, an easy way to avoid this issue is to supply a stipend to the publisher in advance (say, for $5,000) to cover the cost of their "gifts." This way it looks as though they weren't bribed in any way, and were instead paying for a service to have such intimate access to the game and its publisher.
Granted, it really depends on whether the outlet/publication can even afford to give out a small stipend. If they can't, then taking that gift is just shitty and ethically questionable at best (assuming they don't resell off the gift to fans/readers, or reject it).
That is a good example but I think very few companies do that.
The thing is, the quality of the final product (in this case a game review) can and should be scrutinized. But no matter how well written a review is, if it's known that 1) something like the Nexus 7 is given to the pub or writers at any point and 2) their review ends up at least on the higher end of favorable, I would be suspicious of the actual quality of the game.
I'm not saying they shouldn't be scrutinized. I'm just saying a well written review is always a good sign I can trust the writer. Even if the review is favorable or not, I know I'll come back for future articles of this author knowing I can trust him. Of course, you can be suspicious if something like that happens but as I said again, the quality of the work should be able to dispel your doubts.
Personally, I think people should always be suspicious of the quality of any game as games are very subjective. In general, reviews are there to ease or prove your suspicions, granted, you trust its content. In the end, you will always be the judge.
And there is a lot of corruption in most of those industries. And you cant truly know how much it effects you long term, when you are constantly dealing with the industry more so then the consumer(Just like TV advertisements). Also, games are incredibly subjective, so the idea that you can prove you are not a industry shill through publications is incredibly hard to achieve and for the most part is fantasy ,imo.
Corruption is always there as you cannot fully eliminate it in those industries. It also happens in work and personal relationships, though, it's not that obvious. If you don't trust in the industry anymore, don't rely on them. You will come to a point that the only thing you can trust is yourself.
Though I agree with you that games are very subjective, reviewers are supposed to gain your trust using their reviews so you will come back for more. The decision of them being a shill or not boils down to you. It's very simple. If you like them, come back to them. If not, don't give them their ad revenue and don't read their articles anymore.
So then are you saying that the publishers are receiving no net benefit from doing this, that they are wasting money, based on nothing and they don't have anything in office that shows a net benefit from gifts, events, and ect? Because that is what is truly hard to believe, that these companies that have billions just straight up waste money at press events giving stuff away and ect, simply because, it just doesn't make sense.
The net benefit of doing this is not as tangible as you may think. I think most content providers want to establish a good impression and a relationship with those people on the receiving end because they want those people to think of them in a good way. It's the same thing as providing a sales pitch to a certain client. You treat them to dinner and other things because of the same reason I provided above. Though, it doesn't work all of the time, there will be a point that the receiving end will subconsciously think of the content providers before doing any good or bad decisions related to them because of goodwill. In the end, it will all come down to those people (reviewers/writers) as they should be professionals in what they do.