Argument from authority is not necessarily a logical fallacy. Courtrooms use them all the time in the form of expert witnesses, but not everyone could be an expert witness. (If I were to ever get my P.E. license, *I* could be an expert witness.) And being an expert witness on one topic doesn't make one an expert witness on all topics. Unlike on NCIS, it is highly unlikely that the person who is an expert on fingerprints will also be an expert on bomb residue and computer forensics. It's not a perfect system and the standards are completely insufficient, but standards do exist. The NAS has recommended improving the standards.
The argument that many religious people make runs something like this:
"HO! Einstein believed in God! He's the SMARTEST GUY WHO EVER LIVED and HE said God exists! You think you're smarter than EINSTEIN?"
Of course there are a number of problems with this. First, few people doubt that Einstein was a smart guy, but what makes a person an expert authority on God? What makes him more knowledgeable than anyone else? Second, did E really believe in God? And third, if E did believe in a God, what did he mean by it? Not always - but most of the time - the person making this claim is implicitly (and often explicitly) arguing for an Abrahamic type god - a conscious god who pays attention to us, cares what we do, perhaps even communicates or otherwise interacts with us. Fourth, there are and have been other people who were equally smart who have clearly been atheists (Richard Feynman, for example).
I'm reminded in this of the quotes of Darwin taken out of context that demonstrate he refuted evolution or legends of his having recanted evolution on his death bed - as if knowledge has been stagnant for the past 150 years and the only reason that anyone ever accepted evolution, and the only reason anyone accepts it today is because of Darwin's expert testimony.
