Wow ~ I hate to feel as if a 'Get Chinny!' bandwagon is forming but...
I just talked to an acquaintance who specializes in litigation concerning misrepresented items' sales.
According to him this type of situation falls directly under his specialization.
It's true the buyer had the opportunity to research into the specific nature of what he was buying. Had he but searched the threads and found any of the several locations where Chinny discussed the intermittent issues with the tweeter Diamond would have known better what he was getting himself into. So...he had the opportunity...but not the responsibility. It is the right of the buyer to take what is presented to them for sale at face value and believe that they are getting what they've been told they're getting. Doing so may not be the smartest course in all situations (as has been proven here) but it happens.
The seller, on the other hand, does NOT have the discretion to fail to disclose to a potential buyer any known defects in an item presented for sale. Using a defense of 'the defect didn't produce itself this time when I checked so I reckoned all was well' wouldn't fly very well in court and could potentially be viewed as fraud.
Chinny, I don't know you so I have no personal agenda against you, guy, but I'd have to say it's on you, mang. You didn't tell the man there was a problem with the comp set but yet told many others there was. Refund the man's money and get your gear back.