Ideally, you dont' get yourself into a situation where you need to disclose anything.
If that isn't possible, you at least disclose things.
That is still bad. That shouldn't be the situation, to begin with. But if it is, disclosing it allows the audience to understand the possible (and likely and unavoidable) potential bias.
Getting free product to run your site is bad (unless maybe it's a sort of endorsed sponsorship and you are public about it -- sort of like a race car driver's sponsorships).
Getting free product to review is not ideal, but is pretty general practice and considering the expenses involved in products, can be the only way a reviewer can get the products in time (often before release, so they can inform customers) or even at all... because budgets are limited. Again, not preferred, but not inherently "vile" or anything.
Paid reviews... are obviously bad. Under all circumstances. A paid review is not a review; it's a commercial.
Close affiliations with companies you cover is bad. You recuse yourself. If you can't, you either provide full disclosure (doesn't eliminate the bias, but informs the audience) or you skip covering it at all. This as well as the things above are covered by pretty much any first day journalism class. Even a junior high student should understand these things. They were also covered at SPJAirplay for those who needed a more authoritative "no, that stuff is bullshit, this is what is ethical". Being buddy buddy with the Corsair guy that you know by first name is generally frowned upon. Unfortunately, that is much of the state of tech and games coverage these days. You become close (either professionally or even personally) with people that you deal with in the industry. Then you have to cover them or their products or their company. Are you going to be as unbiased about their company doing something shitty, having a terrible product, or feeding customers a line of bullshit... when you talk to them every few days, are invited to events by them, or hang out with them on the weekend? Fucking of course not.
Of course, Linus started his gig off by doing tech videos for a his employer who sold computer equipment... so I've always taken everything he had to say with a lot of salt. I generally believe him to be a trustworthy and well-intentioned fellow and would find outright payment for reviews to be unlikely, even if there are other no-nos like "being too close to the people we cover" or, you know, their sponsorships. That isn't unique though. And I do find it gross. When I go to see a review by some tech group on youtube and their videos start off with a big add for Corsair or CoolerMaster, I know they are going to be influenced (again, you can't help but be even if you know better -- that is why you don't fucking do it...potential impression of impropriety is just as bad and should be avoided just as much as actual impropriety).
Anyway, I like Linus. It has been fun to watch him grow and evolve. I would be incredibly shocked if it turned out he was involved in anything truly shady. However, knowing the difficulties of a small business owners trying to keep from going under, I would not be shocked if there were some unwise decisions that have to be accounted for (like accepting hardware to run your site from a company that you might cover at some point, for example).
In cases like this, a lot of it comes down to the faith you have built up in your audience. The credibility you have earned. The problem is, you should not put yourself in situations where you have to rely on your past credibility to explain-away or account for current potential bias.
If this were anything outside of product review worlds... it would be absolutely cut and dry. You would not be allowed to cover a political campaign via a laptop that the campaign gave you. You would not be able to do financial news on the tech sector via a laptop and cell phone that were given to you for free from the tech sector.