It starts with learning to decipher the proof marks. And for those, you just about always have to ask for pics of the proofs. Usually not among the pics on the site. However, you also don't want to be inundating them with pic requests. So without being able to be super specific, I look at the shape of the action and bolster as well as the style and quality of any engraving. There is a different look to the prewar guns. The post war guns were basically all made in the same factory with the same forgings ending up looking very similar and just had different names put on them. That's an oversimplification but not by much. Pre war, Sauer and Simson were very different companies making very different looking actions. Huskies, just look for a model 310.
Most of these guns on Intersurplus (and similar retailers) are post war guns. So for example, look at all the Sauers and note the similarities. Then try to find a Sauer that just looks different in some way. That's the one to request proof pics to confirm.
Damn......I'm giving away trade secrets!
This is a Greifelt, made in the 1920s, bought from Intersurplus for under $400. Likely used a Sauer forging.
This is a Ferlach made (Austrian, not German but that's splitting hairs) in the 1920s. I think I paid $450.
On both guns, note the fine engraving. Now look at most of the Sauer/Simson/Merkels on intersurplus and check out the engraving. The difference should be obvious. Once you see it, you can't un-see it.
