I sold a couple of Zippo's on ebay. Some were unit marked and some older.

I got from $6.00 to $42.00 for a mint zippo in the original box with documents from the 40's.

I hope that helps you price it.

Please keep in mind that during WWII a lot of GI's smoked and they all had zippos, so there are a ot of them.

http://www.worlddaggers.com/