Selling dispute. Please comment.

I recently sold a pair of mono amps and checked the box that indicated the original manual was included. I never use the manual for something like this and just assumed the manual was in the box as there were some various papers from the manufacturer in the boxes.

The buyer got the amps safely and they are in perfect condition as described. I shipped the same day the item sold. Unfortunately the manuals were not in the boxes the amps came in. These were the original boxes, but the manuals are not there according to the buyer.

I sent him the link to download the pdf of the manual. He is not happy with that. I offered to print a color double sided copy (on good stock) at Kinkos for $20 (at my expense) and ship that to him. He says that the original manual was promised and that I have to deliver that to him. And that he dervers two of them since the amps came in two separate boxes. He is threating to kill the deal and dispute with audiogon and paypal.

I admit that I'm in the wrong for mis-stating that the manuals were included. I will attempt to order the manuals from the manufacturer on Monday, but I don't know that the manufacturer will provide them even if I pay for them.

I'd appreciate comments regarding this problem. Thank you.
No other lawyers here? Seller substantially performed, so Buyer has no right to reneg or undo the deal after delivery. Damages are calculated based on the financial loss the Buyer incurred due to Seller's inadvertant misrepresentation, which in this case, are trivial, or the difference in price between the value of the item as represented and the value of the item as delivered, which again, is a trivial difference. This is not the same case as a unique antique or collectable, where specific performance can be the applicable standard.
I would refund the money, MINUS shipping. The guy is being a prick, plain and simple. Once you get the amps back and verify they work, I would then give the buyer NEGATIVE feedback to let everyone know what a picky bastard he or she is.

He is really just looking for an excuse to get his money back. He is buying USED, so one should expect things like this.
What if buyer is a liar just trying to get some unreasonable discount or has buyers remorse?
Since this is the most anal hobby known to man I would be a bit bent if something didnt come with the manual. I always like to have the original boxes, manuals & if possible original purchase receipt or copy of the receipt. It makes me feel that the product was treated with the respect it deserves. Like others, try to buy the manuals. If they come in photo copied from the mfg, see if they will give you a letter that states this is what they originalally supplied. If thats what they were/are and the buyer still doesn't like it, then they're just being an ass. Good luck, John
Perhaps the buyer has an alterior motive in wanting the deal cancelled and is simply using the lack of manual as his out. If for some reason he was disappointed with the amps (sound, looks, smell, etc.), he may be trying to reverse the sale due to his buyer's remorse. Integrity is subjective, and with some, totally absent.