Sorry this happened. Most buyers on eBay are honest, and most sales are pleasant experiences.
Let me start off by saying that a helpful attitude in these situations is to view eBay as your enemy, and not the buyer ... the buyer is simply trying to take advantage of liberal return policies that eBay established and enforces. I say this simply because it is rarely productive to get into a battle with a dishonest customer ... they just heap more dishonesty on the situation. Focus your energies on eBay.
Your situation is not hopeless. I am assuming that you have not yet refunded the money, correct?
Possibility #1 - The buyer has admitted in eBay messages to dropping the light, prying open the light, installing the light, etc. They cannot do this and get a refund. If this is the case, I would go ahead and call eBay customer service and point out these messages to the Customer Service representative ... you should win this case, and not have to refund.
Possibility #2 - The buyer is claiming that the light arrived damaged/broken ... that is, it was damaged in shipping. If this was sent first class (as your listing says) without insurance, then there isn't much you can do. You could, like #1, complain to eBay, but they are going to side with the buyer most every time on a shipping damage claim. They will tell you that it is your responsibility to pack well, insure, la la la la la.
Possibility #3 - (Similar to #1 ... you are trying to win based on the buyer opening up the light, solely on the evidence of the photographs). This is a long shot, but thought I would mention it.
If the buyer's photographs clearly show damage due to opening it up, and your pre-shipment photographs do not have that damage, you can challenge the return claim <<<OR>>> the buyer's photographs are of an entirely different light ... that is, the buyer is attempting to commit "switch fraud" (this is where a buyer purchases a working item, and returns a damaged or defective identical item that was previously owned)
Based on photographs alone, you will likely lose on the initial claim simply because in "he-said, she-said" cases, the buyer is most always rewarded with the refund. However, your strategy here would be to appeal the initial decision and escalate it up to someone who actually can make a reasonable assessment ... a supervisor or other very experienced customer service representative. Your success will really depend on who you get.
Keep in mind, if you challenge a return and lose (exhausting all appeals), eBay will punish you with a "seller defect" and they will not refund the fees that they collected on the sale (about $40-45 in your case).
