Is Appeal to Authority Ever Acceptable?

[Tiberius]

I take issue with the conclusion that "x is true". We are talking about people here, and people can be fallible.

Wikipedia lists a better form:

X holds that A is true
X is a legitimate expert on the subject.
The consensus of experts agrees with X.
Therefore, there's a presumption that A is true.

In essence, an argument from authority is always fallacious if you use it to conclude that something must be true. Wikipedia handles this one nicely as well:

...because the argument is inductive (which in this sense implies that the truth of the conclusion cannot be guaranteed by the truth of the premises), it also is fallacious to assert that the conclusion must be true. Such an assertion is a non sequitur; the inductive argument might have probabilistic or statistical merit, but the conclusion does not follow unconditionally in the sense of being logically necessary.

https://en.wikipedia.org/wiki/Argument_from_authority