Well, I think the important thing here is 1: to not wallow in the fallacious belief that, because one removes the back of something that it's ruined or permanently altered. Having bought and sold a lot of those things here and elsewhere, I know from experience that it's always a good idea to at least look inside if you have a chance. Not that the seller or buyer feel that way, or aware of the risks and hazards... but it's still true.
And 2: all participants should come away from this with a lesson. Like, "good photographs are paramount," for example. Or "clarify before bidding whether this is the item I want to buy." Had the photos been clearer, the buyer would have seen any alleged scratches. And judging from his responses, I doubt his take-away was "I can ignore good listing practices and rely on buyers' mistakes to make the sale stick."
It was only much later that people started bickering over whether or not one should "take something apart" for any reason before returning it. OP admitted to taking it apart first, remember. There's a good chance his buyer might be even more knowledgeable than he is, and is following up on someone else's work. But it seems that some here just put the buyer in an inferior position by principle, which is just as bad as eBay's common practice of putting the seller's reputation on the block at the whim of the buyer.
Suppose for a moment the buyer took it apart and found that the repair work had been terribly botched, or that it was badly corroded because someone spilled Zima into it when the Broncos won the Super Bowl. Yeah, the seller could respond, "well, you pays your money and you takes your chances," but that's not necessarily what anyone would do. There's a difference between "resolving" a dispute and "winning" or "losing" a dispute. One approach leaves people bitter from the experience and the other does not.
I doubt either party would take the same exact approach if they had it to do again.
