Thanks for all the suggestions. We are both pretty reasonable so far and are trying to work towards a fair resolution for both sides. We will see what LUX says as far as repair costs and determine whether it makes sense or not.
The buyer has been pretty patient so far and we both have good communication so I am confident we can work something out.
Unfortunately, it is a scenario where we can't prove it was working before or not but neither side is pointing fingers here, we just want a fair resolution. Lesson learned, document and test better prior to shipping on my part. I have been to LTBMW's shop several times and I think he would have pointed out, your Angel eyes aren't working or aren't bright at all, what's wrong? I'll sell you a new one.
But I did inspect each item before testing, I just never had a problem in selling anything before, I didn't expect one here.
I have an ebay rating of 82 with no negatives and have done several, several transactions here. I have many people on this forum that know me personally and can vouch for my character.
The most important thing is both sides are working towards a solution. I thank the buyer again, for being patient while we figure out a fair solution.