[lugerholsterrepair]

Hard to say with the economy the way it is..the last one of these I know about sold for $25,000 here in Arizona about 5-6 years ago.

I authenticated that one and have done several Krieghoffs since. It was discussed on the Jan Still forum and some collectors thought it was a fake. I went through that pistol with a fine tooth comb and if it was fake I would dearly love to shake the hand of the man who did it. That would be an honor. If it was fake which I don't believe.
Not many people are knowledgeable enough to authenticate these or any Krieghoff for that matter. It is necessary to dismantle many of the hidden parts looking for markings and numbers. Comparing fonts etc. to what should be there. I am unsure who I would recommend for this.. Off the top of my head I can't think of many people I think could do it or that I would trust for any accuracy.
Ben already mentioned Simpson's Ltd in Illinois. I doubt there is an experienced appraiser with a good background in Krieghoff Lugers there. If there is one who is he? He is hiding from the Luger collecting field...
Dwight Gruber comes to mind. Ron Wood is a likely candidate..George Anderson too. What would be ideal is to have 2 or 3 people in one place to brainstorm it! Any three of these Gentlemen could make their own recommendations I am sure.
Anyway it's quite a find. Congratulations to your Friend.