There are a number of sellers from Latvia selling WW2 German helmets as originals.  They are taking relic  helmets and original shells in poor condition, painting, artificially aging, and adding reproduction liners/decals.   If you receive a helmet and you smell paint, it is a bad sign.  Original authentic helmets have a very distinctive old smell.     These helmets also come in very dusty, especially on the inside.  That dust is body shop dust to make the helmet appear old.  The rusty shells are often splattered with a oil based material that resists the paint.  Once the paint drys, it is wiped down, leaving rusty spots.  Most of the Latvian remakes have odd spots of rust, and a greyish dust hue.   

The sellers often only accept Western Union payment.  Yet another Red Flag.   Beware of contrived positive feedback to give the illusion of being an honest seller.   They create this thru very low value purchases to build quick positive feedback.  They are also very quick to change Seller ID's.   Many new collectors fall prey to this scam.   These sellers also use software such as Activa for pictures that cause the pictures not to be available after the auction closes.   There have also been instances of these sellers sending pictures of Authentic decals that they have pirated off of a website, then sending the fake helmet in it's place.      They are also selling fake liners.   All of these liners look very much the same and have a greyish look, reason being, must of the shells that are being recreated do not have liners as they rotted away.   The liners often will have very red rust on the liner bands.   Buyer beware of this region.  

Another red flag is they hide their feedback and often hide the bidders.   And lastly, they love to say things like, "from an old Russian Museam" or "found in an Attic".  

Additional note: 

There are several Ebay sellers in the US that appear to be acting as fronts to give folks the Warm fuzzy that they are buying from a US seller.  Same helmets, same story, using the same disappearing Activa pictures, same storys of "vet estate" etc.