First of all I'm not an expert and only have one example myself, so this is just my opinion.
The colour on the outside looks correct, the inside looks like the colour adopted by the Belgian army post WWI, the chinstrap looks new, the liner is original and is the first type 7 leaf version. I thought (I'm not sure about this) Belgian liners had khaki coloured cotton and French liners had red at the beginning, later changing to blue.
I can't comment on the badge being original but it looks the same colour as the shell which is positive in my opinion.
All in all and going by the inside colour as well as the remains of khaki on the lion, I'd guess at it being an original WWI Belgian helmet that was repainted in the 1920s, the green 1920s repaint has since been removed on the outside to reveal the original colour, an original French first pattern 7 leaf liner has been added as has a new chinstrap.
Hopefully someone who knows more than me will be along to give you confirmation.
In the meantime have a look here .: World War Helmets - Belgique :. and liners half way down the page here .: World War Helmets - Casque Adrian modèle 15 :.
all the steel parts are original,not sure on rest.
Thank you guys, I will consider buying it if the price is right. I contacted the seller and he said the chinstrap is a repro.