I can't attest to a different odor. In fact, I can't detect any odor in the metal other than the lubricant and preservatives I use...
A few years ago, I purchased a copy of an old book,
The Art of the Faker. It mainly addresses faking artwork, but is broad enough to cover other collectables. It's discussion of the psychology and motivation for faking things is quite interesting.
As we're all familiar with Ted's outstanding restoration work and his ethical approach to properly documenting restored firearms, we can appreciate that the skill and application of quite a bit of labor can result in very high quality results that could be hard to detect.
The problem is that there are those with skills and motivation but without the ethics whose objective is to deceive. Thankfully, very few people have complete knowledge of Luger variations and the fakers make mistakes that can be detected by those with enough experience. Sharing that experience is one of the highest values of this forum.
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Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.