Considering the rarity of anything genuine from Simson, if it has the period correct magazine with a genuine E/6 inspection mark, I'd probably buy the pistol.
Remember that only 12,000 or so Simson Lugers were made, and perhaps 24,000 magazines would have been produced for those pistols - total.
IIRC, It normally would have a folded tin body, and E/6 marked aluminum base.
Legacy recently sold this one:
https://www.legacy-collectibles.com/...032819-03.html
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Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.