I've bought 3-4 times at egun before, but just spare parts and stuff, never a gun.
I guess it would be a real hassle to import a gun into the US if you buy from a private seller. The most sellers just sell just within the EU, a dealer with experience will maybe sell out of the EU, too.
If there is a reserve, then you can see it right away:
This Luger, for example, has a reserve of the amount of 900 Euro, it's the starting price for this auction. I have never seen a "hidden" reserve price.
Sometimes Lugers sell really cheap in Germany, especially if they have no modern proof markings. Then they have to get a new proof mark before they can be bought by a private buyer. Only a gun dealer or a collector (with a proper license) may buy one of those guns. Alot of old WW1 and WW2 guns have no modern proof markings. Then there is another reason for cheap prices: In Germany it is really hard to get a license to buy/own a gun. Alot of the weapons are from people who enherited a gun and must sell the gun because the gun license office give them a hard time, this reflects on the prices as well. Alot of them just want to get rid of the enherited gun/guns.
Sometimes they just give them away for destruction, just to get rid of it.
(BTW: There are about 20,000,000 (20 Million) estimated UNREGISTERED (illegal possesed) guns in Germany, too. That's alot.
But only registered guns can be sold on egun, of course.
http://www.egun.de/market/item.php?id=2632519