I've got several similar ex WD sledge hammers but I haven't bothered to check the dates to see if they are wartime or not. Things such as this continued to be made after WW2, into the 1950's, like the "BritishArmy Spade/Shovel" to exactly the same design as it was in WW2 but with a WW2 date it is much more desirable. Armoured vehicles carried them like they carried a spade/shovel and other tools but it was also used for other applications that required a sledge hammer.
I would have thought on your side of the pond, if the handle is reasonably good, about half the asking price because there probably isn't many of them in the US and it's WW2 dated.