You're contradicting yourself. You say there's nothing else you can tell them and then you say you email them a scan of the grading label and a complete description. Which is it?
You don't have full disclosure in the listing. What exactly is the problem with putting in the listing exactly what you emailed the people who asked you about the thing?
Put a scan of the grading label and a typed descrption of whats on it in the listing. THAT would be full disclosure.
Why are you so averse to doing so? That's what myself and others are saying is the problem here. You have to do that. Not doing it is NOT giving full disclosure. And I'm not saying I think you're deceptive. I'm saying potential buyers could think you're being so. I think you're being lazy taking the easy way out and not putting all the info in the listing.
Generally when people sell stuff of high value they take the time to put all info in the listing. Especially any and all defects and close up shots of the item from all angles. It should be done with all items but especially those of high value.
You're missing the point saying he receieved what was described. You're relying on little to no description of the item to fall back on to throw in the buyers face. It'll come back to bite you in the butt sooner or later.
What you're doing is akin to someone selling say a 1982 Volkswagen Jetta. Blue book value of $X with no other description. (I don't know what they're worth) and giving NO details about it. Someone buys it and there are tons of problems with it. In theory they got the 1982 VW Jetta yes but the seller did not put a full description of the condition of the Jetta. And therein lies the problem.
When you find doing what's right hard to do - you've got a problem.