It is not as a general rule irrational to place some degree of trust in expert opinion if that expert opinion is informed by the scientific method. This is because the success of the method is irrefutable. And to the extent that experts adhere to the scientific approach and submit their work for peer review, we may assign some credibility to their work. If every physicist on the planet says x is true, I had better have done the research before I attempt to refute them. We do not have time to become experts in every possible field, but we know the methods of those who are, and we can see whether knowledge is generally arrived at through sound reasoning in the scientific community for example. We also know the methods of the Catholic Church, which is why we would not be rational to assign their authorities a high degree of credibility in matters of, say, the origins of the cosmos.
Ad verecundiam is not a generally reliable method for establishing facts. But the agreement of many scientific authorities does to my mind tend to increase the probability of something being true, though evidence will be the ultimate arbiter of truth. Let us say that I will assign more credibility to a proposition (provisionally) then conduct further research to test whether my credibility is warranted.
The key here is "further research." Opinion is no substitute for research. Aristotle was wrong. Ptolemy was wrong. Galileo's academic contemporaries were wrong. To quote Feynman, "The test of all knowledge is experiment. Experiment is the sole judge of scientific 'truth'"