My concern would be the dry rot to the neck guard, that makes it very, very fragile. I have one like that and you have to treat it very carefully. You might ask the owner if he has photos of it with its plate off and the back of the plate itself. Look at the photo of the front plate, it looks as if there are two marks in the shell by the 'shoulders' of the wings (are they holes or is it bare leather????)... although the imprint of the head looks good in the lacquer and the inside looks okay with no holes there. I'd ask for more photos.
It's odd how the cockades are rusty and the helmet itself has dry rot on the neck guard. However, it all seems to fit okay since it's possible that it was moved from a dry to a damp environment. I'd say get more photos of the plate / behind and it will probably turn out to be good.
I really like this one very much!! It has this very special "optical" touch of such objects which have a story to tell, because they have been worn intensive. I already can smell the leather and the old metal patina. :thumb up:
Philippe