It may well be that the mechanism they're using isn't really duping, as in they have an item and they make copies of it. Maybe they're figuring out some basic code-level thing they can slip into their communication with the servers that makes them think that there's a particular item that shouldn't be there in their bags after executing a trade or looting or logging out. Or something else, I dunno. It doesn't make any difference from our perspective, but it would kind of explain Blizz's reluctance to call it duping.
What really bugs me about this is that, as someone who likes collecting this stuff and tends to watch the market/AH fairly closely (and that's probably true of a lot of the people here), I seem to have an uncanny knack for getting screwed by these events. I know what a good deal is on a lot of these items and when they first pop they're at like 80% of the best price I've seen in a while so I'll pick one up, little realizing that it's going to drop to 20% over the next week. I can't really think of a good solution for it either. I could be more suspicious about the person selling, except that sometimes they're just on the AH, some people use level 1 alts for bankers and some exploiters are selling from hacked level 90's. I could stop buying things that seem to be a good deal, but that's just a different way of losing money. I have plenty of gold and am pretty good at earning it, but earning 50k still takes a non-trivial amount of my time. I can only imagine what it's like for someone who isn't really into making gold and has just decided they really like one particular vanity item.
I also wish blizz would devote more effort to protecting the economy when these things come about. It doesn't seem like it would take that much manpower to throw a serious wrench in these operations. Even if it was technically difficult to catch them in the actual duping act, just chilling in trade chat on 15-20 or so of the biggest servers looking into any accounts offering these pets and dishing out some short term bans would do a lot to reduce the harm until the problem could be fixed more permanently. I'm assuming that the accounts being used by the actual gold sellers look pretty suspicious.
I guess at the end of the day it's only a fairly small number of us who are really hurt by these events though and we're fairly well situated to take it in stride.
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