I do not often browse the ebay listings anymore. While you can find genuine material, it takes browsing through an overwhelming amount of forgeries and uninteresting stuff.
Here some highlights of the bad kind.
All cancels fake. Most of the base stamps forgeries.
I can see one genuine overprint.
Quite high price tag.
I think there is not a single stamp with a genuine overprint.
And you can spend a lot of money on worthless forgeries.
I have see the following. An interesting collection if genuine.
http://www.ebay.de/itm/Armenien-Armenia-1919-1920-alte-Sammlung-teils-gepruft-/182289754519?hash=item2a7150e997:g:yAkAAOSwOyJX48u8
The collection is contains stamps with genuine overprints, but also a lot of forgeries. However: Richter is not an expert in the sense we use this word today. You can find the following informations on http://www.filatelia.fi/experts/
Georg Richter This very common expertising mark (genuine or forged) is usually considered to be of little value as it is frequently found on forged stamps. Dealer 1943 1949 (Kyllmannstr. 22a, Berlin-Lichterfelde West). This 1906 cover is addressed to Georg Richter.
Regarding stamps form Armenia this is definitely true. The signature is no help/hint in checking for genuine overprints.