You take it on trust that they did these things correctly, and focus on whether their conclusions are justified from their data.
If reviewers take so much on trust, how much more so readers, then? There are very, very few actual standards of technical proof that are in play here.
Particularly when a paper says something that isn't particularly novel. If the results match "prior probabilities" from the literature, the paper will be believed without much question. If it doesn't, it will get more scrutiny. People quickly learn that it is easier to publish when your result fits the status quo.
Take a look at slide 10 of [1]. There are numerous examples like this where physical constants were first measured as a value, and gradually trended up over a long period of time towards today's "true" value. If the experiments were really independent, they would, generally, scatter randomly before converging on the true value. The fact that they did not, suggests investigators were using methods to "smooth" the difference between their data and prior findings.
And thus, we get self-perpetuating cycles of groupthink. And that, in turn, is why supposedly independent experiments cannot so easily be taken as independent points of evidence for an overall hypothesis.
[1] https://www.pas.rochester.edu/~sybenzvi/courses/phy403/2015s...