Obviously, Jeff Gerstmann's firing from Gamespot years ago was an example of corruption(which was seemingly rectified to his satisfaction). Though, we'd likley be fooling ourselves to think that highly-publicized example is the only time an advertiser ever successfully influenced a gaming outlet.
Really, the advertising angle of the gaming enthusiast press has always been a challenging issue, as I think many would attest to. Though, a lot of these examples have less to do with willful corruption than potentially detrimental influence. I think the ethics of "sponsored" posts are questionable. And when a site is plastered with huge banner ads and even video ads on their site above a glowing review, it raises understandable concerns. Timed exclusives for reviews and blacklisting are also potential issues which reveal the tough spot many outlets are in to keep up with publisher-favored outlets.
I'd consider "official" gaming magazines to have been an example of corruption to some extent. For a lot of people while growing up, stuff like "Nintendo Power" or "Official PlayStation Monthly" were hugely popular and their main source for gaming news, and these were -official- sources. I even loved these magazines, and looking back, it's so obvious how much they were designed around promoting the official products and guiding you toward the biggest new games. You'd open up EGM and find a full ad for the same game reviewed on the page next to it. The official magazines got favorable treatment and became almost necessary purchases to keep up on the latest and greatest in gaming. Unfortunately, so much of it was hype, hype, and more hype.
Now we've still got Game Informer, and that's part of GameStop's promotional wing. You think they'd sell it in stores if it wasn't driving more sales to them? Sites at least have some genuine autonomy to decide for themselves, but stuff like Game Informer couldn't survive if they were too critical of games. They wouldn't get exclusives and they certainly wouldn't be sold on every GameStop shelf. That doesn't mean every review in them is necessarily corrupt somehow, but it does raise concerns which should be taken into account when reading it.
I've heard a decent number of people say "games journalism" was better when it was simpler back in the 90s, and that couldn't be further from the truth. I may have enjoyed it back then, but that's because I didn't know better. The current gaming enthusiast press is so far better than what existed back then. All the top sources were official, and I doubt a Nintendo Power reviewer could keep their job if they didn't like a Mario game enough. Just think about how often these sources portrayed their coverage as some kind of objective take on games and reflect on what folks are saying now.
Do people really think outlets back then would have been so willing to muck up the favor of publishers out of concerns they had about sexism or racism? Or the social messages and perhaps gross aspects of games? Recent willingness to actually question developers and express individual opinion has been a boon to efforts against potential corruption. The big concern of corruption is collusion with game publishers and advertisers, not with a writer's willingness to criticize them and potentially step outside the norm by giving a big new game an unfavorable score.
If anything, reviews are still -too- homogeneous, and things like Metacritic and the way some companies are tying bonuses to review scores is bound to lead to more problems as we move forward. The way reviewers are sometimes flown around to fancy places to get "early" opportunities to review games or new consoles is suspect, as well, and there's a reason Giant Bomb has shied away from a lot of that in recent years. For new people getting into gaming coverage, that is especially a concern, because these are willful attempts to influence reviewers and get more favorable reviews and higher sales. It isn't known corruption, but they are things to be concerned about.
It's also worth mentioning YouTube sponsorships at a time when more and more people are looking to YouTube for their info on games. The fact is, that is basically the wild west of gaming coverage, and it is -known- to have serious reasons for concern. For a young guy posting some videos online, a publisher reaching out to offer some swag or sponsorship is bound to have some influence, and if they aren't very upfront about it, viewers will hardly know. Placing [This was sponsored by such and such] in your video description isn't good enough. There are some real reasons to worry when looking at YouTube and smaller blog coverage which is ever-increasing in their influence. For the most part, this open opportunity for anyone to garner that kind of influence is bound to end up favoring publishers with plenty of money to toss around. And this is the area of coverage many expressing concern about corruption lately are pointing to despite them being one of the more potentially problematic areas of coverage today. That is worrisome.
We've seen an end to a lot of the actual corruption in gaming coverage, but since many people have good memories of simpler times, that's somehow seen as less corrupt. I can actually trust individual voices now; I can't say that about gaming coverage back then. There are still plenty of concerns today, but a lot of them are the same advertising concerns as ever or they involve newer, more casual voices. There is plenty of evidence to suggest that publishers are as interested in influencing coverage and scores today as they ever were, and that is likely going to continue to be one of the most important areas of gaming coverage to be mindful about.