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.