You never said in your first post if the unit was in working order for you before you sold it. Nor did you say if your eBay ad mentioned anything about "May not be in working order". You skirted the issue by saying things like "Do I look like Best Buy?"
If you were honest in the ad and dealt with the guy fairly, then fine. What you've done so far is not wrong. I have no other suggestions other than the obvious - try the A2 with different discs. Try it with HDDVD discs and with standard DVDs. Don't even put a disc in the A2 and see if he can access the players menus. He should take the results of these tests and do some Google searching or call Toshiba for advice. If you want to help the buyer with this, that would be great, but not required.
If you knowingly sold him a defective player, then no amount of "Do I look like Best Buy?" and "Please don't moralize with me" proclamations will magically turn you into a decent person. That battle would have already been lost. I do not buy or sell things on eBay myself. I wouldn't even consider it, given problems like the above that can occur. This sell has turned into a problem both for you, and the buyer. Personally, I would feel obligated to take back something I sold to somebody as a working item that turned out otherwise. Even if it worked for me when I sold it. That's not saying everyone feels this way, only that I do. The buyer could be trying to scam you, or you could be trying to scam the buyer, or it could be an honestly discovered problem with the player. You take these chances when you buy/sell on eBay or otherwise on the used market. I think the normal expectation is that a used item will work fine when you initially try it, with no guarrantee after that. Unless clearly stated otherwise in the ad.