You haven't lost credibility with me.

Okay, maybe you can't see into a buyer's mind but you are understandably upset and we can see enough of a pattern here to suspect you have been treated badly or scammed.

For starters, you are a zero feedback seller. That screams newbie to a lot of buyers. They expect you may not know your way around ebay all that well and some buyers will take advantage of it.

Next, you had a very expensive item on sale. And you were allowing an overseas sale. That is always highly risky, you would be better in future (if you do use ebay in future) to limit sales to within Australia only. Much, much easier to deal with if things go wrong.

Then, we have your suspicion that parts of it were not in fact matching what you sent, it didn't match your photos. That's a huge red flag, right there. If you are correct, this buyer always intended to make a claim, swap his broken bits for new and then get a refund.

But the biggest red flag in my opinion is you have a buyer of a $1800 item who has supposedly received some parts broken, yet he doesn't respond to the offer of a partial refund and doesn't respond to your offer of a return either, till 5 hours before it closes. Dodgy.

As far as I know (and I am not an expert on this as I haven't sold in years) you cannot supply a postage label to someone overseas but in a return case, where a buyer says something is faulty, you'd still be expected to pay for that return. The buyer would never get charged for it by ebay.

Now all you can do is negotiate with the buyer privately, in that you can explain that they can find out what the postage amount would be and have you reimburse them before they send it. But that is risky too as I can't see there is any guarantee they would then send it. And he seems to be refusing to do it anyway.

Given the cost of the microscope, he is not being very fair or honest.

I think you have lost your money. You can't do much legally as any Australian laws don't apply overseas anyway. You say your appeals have been rejected by ebay 3 times, so they have dug in their heels.

For your information, you're not the first person this sort of thing has happened to and just about every time it happens, it is an expensive item to someone overseas and the seller loses the item, the money plus is hit with fees. Yes, it is pretty poor ebay awards the buyer both money and free item but the thing is, they expect the seller to sort it out before a case closes. As you have discovered, it is much harder to do this for someone overseas. In Australia, you could just issue a return postage label.

For the future, limit sales to Australia only. 

Maybe sell smaller items till you get a higher feedback score and don't appear such a target for scammers.

If you do manage to get any progress with ebay, let us know.