If the only lessons are "Never trust a seller from former communist block countries" ...
No, this is not the only lesson, thank god. There are also scumbags in Western European countries who advertise their junk on U.S. sites, for example a well known WW2 scope peddler from Italy. I have done business with Eastern European sellers in other fields as well, such as vintage vehicles and parts since the iron curtain came down. In the beginning, they were unloading genuine WW2 articles, then they sold mostly original items with some repro parts, then the large scale fakery started. So, just like you, I did have good experience -long time ago. The problem is, there are very skilled craftsmen in Eastern Europe who have created great reproductions or hump jobs but didn't advertise them as such. Fakery from India, on the other hand, is pretty crude and easy to spot. Here's an easy example for Eastern European craftsmanship:
http://www.ebay.com/itm/German-WW2-Trigger-Guard-for-G43-G-43-k43-with-screws-/263192866313
A couple red flags other than than what is really wrong with this part: a) the price; nobody sells an original G43 trigger guard with screws for $99 BIN. b) not the first time a G43 trigger guard by this seller sold with exactly the same pictures. c) no claims are made regarding authenticity of the part (although "I have for sale WW2 Trigger Guard for G43 G-43 k43" could be argued as advertising a WW2 period item) which makes it easy for the seller to refuse an eBay return based on "Not as described".
While this example is easy to spot as a fake, more elaborate scams like the present attempt at fabricating a Kurz scope or the number of ZF4 "Bu" scope offered in recent years on eBay are more concerning. Same for ZF4 Luftwaffe scopes, very easy to fake. The buyer will find out about it when he holds the item in his hands for closer inspection. Then, returning the item for refund across the Atlantic becomes another issue, especially with eBay. There are too many instances of eBay/PayPal siding with the seller because enough ambiguity was put into the item description, as in the present case where the seller never made the claim for it to be an original WW2 made Kurz scope.
As someone who collects more than just optical sights I have run into several offers where the items for sale were very good reproductions. As long as they are advertised as such (i.e. G43 Durofol hand guard repros) I have no problems. But look at all the MP44 spares coming out of Bulgaria. How many fxo marked spare extractors did Haenel make, how many gas tubes and how many ejectors? And why did they all end up in Bulgaria, of all places? Oh, they got them from East Germany, sure. And why don't these "East German" selector switches fit an original MP44 without additional work?
Are there fakers in the U.S.? Sure, just take a look at the the Gunbroker sellers exposed by ww2weaponsforum. But most of them lack the finesse of Eastern European workmanship. The SS marked rifles by Drago not only look hideous, they look stupid and make the person buying Drago's junk look stupid, too.