I think its going to come down to how you described the stain - you needed to be clear the top was being sold "AS IS", whether or not the stain comes out. So, if youve written something like "stain might come out in wash", or written nothing at all, then technically youre probably NOT covered and will probably be forced to refund - although you could still try it with Ebay.

If you wanted to, you could email the buyer and tell them the stain was listed and described in the listing, if youve written sold "as is", refer them to that in the listing. If not, hope and pray they give up.

However, if you dont refund, youre probably going to get a defect anyway from negative feedback, which Ebay is not going to remove stain or no stain. Feedback is based on customer satisfaction, which is opinion on a transaction (ALL of it), not really hard facts.

So if I was you, I'd email them the above, wait for a reply, and if they complain more offer them a refund. Be happy about it in the email, more than willing to help - Tell them the day you receive the top back in the post, you will refund immediately. Ask them to put tracking on it for THEIR safety because Ebays policy is no return, no refund.  Let them know they are responsibile for return post cost, BUT,  Paypal actually has a return post offer where the buyer can claim! But make sure they read the fine print so theyre covered! (how good are you as a seller for giving a full refund and letting them know about the Paypal reimbursement!!).

Positive feedback is the aim.

Being out of pocket a couple of dollars that you can make up on another sale is better than a neg that wont be removed (depending on how much feedback youve got and how much you can risk it, I guess).

 I have taken on a few neg feedbacks because I knew no matter what I did I was going to get it anyway, or that it was a real scam. You need to judge the situation, buyer and their emails.