This [1] is a fairly great conversation with him which covers a lot of topics including the incentives [2] many other YouTubers/Car Journalists have (from getting flown out to launch events and the general pressures to not lose access to press cars by being too negative in a review)
That said, while I trust Doug far more than many reviewers he still has many relationships with car dealerships, often gets access to preproduction cars that he can't drive yet (but almost always does a full review when he can), and does have a car auction business so there's still room for that to have an effect on his judgement even if he's trying otherwise.
[1] https://youtu.be/pFGh-YqHT4Y [2] https://youtu.be/pFGh-YqHT4Y?t=5155