I agree with everything you just said. But as a matter of practicality, there's no denying statistical probability. If there are greater odds of finding frankens in Ukraine, Buenos Aires, etc., I have a lower threshold for hitting the reject button and moving on. Sure I might miss a bargain here and there, but as part of an initial screening process, if you will, I think certain prejudices and stereotypes when used appropriately, are beneficial.
To give you an anecdote about my position:
I've also lived in Buenos Aires, and am quite familiar with the petty crime and "trucas" or tricks that go on there as a very regular part of daily life--things that most New Yorkers or Londoners would be horrified to think about.
Speaking again from experience, I know that there's also a higher probability that legitimate watches coming from Buenos Aires are likely stolen. A member of my family was the victim of an unsuccessful mugging by two guys on motorcycle. The family came to visit while I was living there and very much looked the part of clueless American tourist. We'd been in a very nice area of town at a restaurant, seated up against the glass windows. My brother, who's a big guy, was wearing a Rolex. On exiting the restaurant the two guys on the motorcycle whizzed by (they'd obviously been staking us out), one jumped off, grabbing my brother and wrestling for his wrist. We reacted quickly, and probably got quite lucky. In no time the motorcycle had made the block and come back to pick up his buddy and he was gone. We found the Rolex lying in the ditch, where he'd used such force that he'd succeeded in breaking the metal bracelet (not from the spring bar, but from the middle of the links).
This sort of thing is an everyday occurrence around BsAs. So you have the antique dealers assembling frankens, the petty thieves that live around the outskirts of the city and prey on tourists, and the high end, legitimate dealers who will have nothing to do with a hot watch. Argentines will do anything for dollars (as opposed to their chronically devaluing peso). So where do you think those watches go? They're sold to other dumb tourists, and they're put up on eBay.