If you want to be 100 % sure, there's a simple rule you have to follow: Never send anything to an European country that looks like a firearm, even if it's just a toy!
Pardon me, but this
generalisation is nonsense and just irritates intl. "reluctant" sellers even more. Do you really want to make it harder for us european prop-collectors?
European laws are very specific AND diverse when it comes to importing "weapons"...
F.e.:
German law states, that as long as an item is not designed to shoot any projectiles/ being a replica only (ALL types of guns, rifles, SMGs, MGs!), it matches the regulations and is free to import (no matter the material it is made of).
Different rules apply for softair, which have to be limited in their power, muzzle velocity, being full/ semi auto.
Rules for importing deactivated firearms has changed a few months ago for all members of the EU. If a gun was not deactivated to the new standards, you´ll be in trouble.
IF you want the business, recommend your potential buyer to get in contact with his central customs office and ask for french import regulations. From what I know, france and germany are pretty similar (unlike the UK) and importing a blaster is not a problem at all.
So the general rule should be: Have your customer insure the legality of importing any kind of item...he´s responsible for the compliance with regulations and potential loss.