ShenTao,
In my view, we are dealing with separate issues here.
One of them is the seller being a jerk, with no concept of customer service, and making ridiculous claims. This goes without saying, and in this light I agree that eBay was right to rule in your favor.
However, seeing as you probably already knew of the seller's record from this forum, this begs the question as to why you entered into a transaction with him in the first place. Because you thought you are getting a rare collectible at a good price, and were willing to take the risk?
As to the "merits of the case" - here I have to agree with the others - it is not as clear-cut as you seem to think. The seller did not misrepresent anything. He never said that it was a mechanical keyboard, or a genuine IBM M13. The fact that there exist out there keyboards bearing the "M13" name, by IBM as others, some of which are not mechanical, has been established. That "the community does not consider them genuine M13s" is irrelevant. It is not the responsibility of a seller to know all the canons of obscure geek communities.
He wrote "appears to be identical". In some ways it is, in others it is not. He did not even make the claim that it's guaranteed to be identical in any way. The way I understand when someone tells me something "appears to be" is that to the best of his understanding, it is. If I know that there can be caveats, that not all people may be aware of, I ask for clarifications first.
It seems that in this case neither you nor the seller were aware that there may be differences in key mechanisms between M13 keyboards, and I don't think that he is more responsible for the resulting error than you are. In fact, had the seller taken a more polite and logical (but firm) approach, the outcome may have been different. His listing did say 'no returns', and your case of 'Not as described' is quite weak. He said "IBM Compatible", not "IBM", and "appears to be identical", not "identical". He posted detailed pictures of the item, which you could have researched, or tried to research. If you could find no useful information, that is still not the seller's problem. I am aware of no rule that says that sellers must know all the obscure tiny details about every thing they sell.
Reasonable sellers would finish "no-returns" listings such as this one with "if you are not sure about something please ask before buying". Then if you did not ask, and chose to buy based on the limited information offered in the listing, the seller would not be held responsible. Obviously, this guy is not a reasonable seller, as is evident from your and others' communication with him, and he does not want to answer any questions.
TL;DR - you are very lucky that the seller is a jerk with poor communication skills. The merits of the case were not in your favor, and a different seller probably could have convinced eBay that he is in the right, not you.
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