re: German Lugar

Trying to find someone that specializes in Lugers and doesn't try to screw you out of yours is going to be difficult. Someone that is displaying Lugers at gun shows may have a lot of knowledge and be helpful. Very few gun shops ive been in had folks that I would trust unless the shop specializes in these guns.
You may have a very rare gun with specific details that sets it apart. Value varies greatly between manufacturers.
Since these guns have been around for over a century, thru two world wars, many have been destroyed which increases the rarity.
How much original finish remains affects value greatly.
Another consideration is the holster - it could be worth a minimum of a few hundred and go thru the ceiling for a more rare model.
The German occupation mark increases value on gun and holster.
I hope you're getting my point. There are lots of books on these guns that may be helpful. At a minimum if your gun has matching numbers it's worth over a grand.
Good luck