The way it works in the camera industry is that you sign an NDA, with an embargo date. This way the manufacturer can orchestrate a coordinated release of reviews for maximum clicks on the announcement day. There is a select few - a handful of people - in each country that are privy to the camera launch details about 2 weeks before the release date for the public and are legally bound not to say anything until the embargo is lifted. However usually always 2-3 weeks before or even earlier, the scumbag rumours sites will leak it all out anyway. So that effectively mutes you on the topic, whilst everybody else is free to talk about it. So the only advantage of signing that NDA is you get the info from the official source rather than the same info from a rumours site. For sites like Camera Labs or DPReview then, it is 100% necessary to get the actual camera early and do your review in time for the launch, otherwise be left out of the circle jerk and launch day manufacturer publicity drive... The review would have to come out a week or 2 after most customers have got the first batch of stock in their hands. Also you save money this way naturally, by not buying anything and just taking loans that go back. There is no enjoyment for me in this, as for me the camera is a personal item and a long-term investment in my work. I only accept a loan if it is long term with no strings attached.
The manufacturers never stipulate that you have to write only good things about a camera. It is an unwritten rule that if you're too honest of course you'll be phased out of involvement in future. Even in feedback sessions and market research you get the sense that some marketing people only want to hear from the yes men. The marketing approach of each company differs. Panasonic is more honest and straight forward. Sony have a tendency to play the big hype game with social media influencers. Canon seems to delegate a lot of their marketing to outside PR companies.
What I enjoy with Panasonic is the technical side, the ability to send feedback direct to the engineers in Japan. I value this very much. I deal with Panasonic in the UK who do a very good job on all fronts and sometimes Panasonic in Germany who just aren't as helpful at least in my experience. After 11 years in this industry, Panasonic are the only company who have stuck by EOSHD and made sure our voices get heard in the development of their cameras. Almost all the other companies I have dealt with see this community as purely a marketing channel to be exploited for their own gain, and not for the advantage of us. Fujifilm in particular, once sent me an interview in a fucking spreadsheet of one line answers and expected me to publish a strictly censored version of it with key questions taken out. Needless to say, I sold both my GFX 50S and 50R afterwards and GFX 100 is next.