I did not go to the link, I am at work, so don't have time.
The main thing is if anything has been refinished.
I can say, that i paid $5,000 for 5 lugers several years ago, resold four and had one to to keep and made a profit. two were shooters for sure, two were collectables for sure and one was 2 matching mags, but had been 'restored'.
A professional opinion is best, but $600 is a low shooter price (non collectable) and up - I would expect if all original, that the value of each (not counting the shooter long barrel) is $1500-$2200 each RETAIL. If original, all matching as expected, and don't assume you'll get high end retail for everything
Ed