Powers on untested. They want a return even though as described

[maxmorter503]

I listed an item for 1000$. took best offer for 800. Described it as powers on untested as it turned on but not familiar with its workings.

Stated I do not accept returns

Seller is asking for a refund. 

They state in 1 message they understand I don't take refunds and they are stuck with it

I have 100% but this is a couple thousand dollar item and probably if taken for servicing will be just fine as it had a 2010 service tag so prob need it

What do I do. I'm out 37$ on shipping over what I charged for shipping as well already. I think they just wanted a part or wanted to try it out and are gonna open a case