Buyer is trying to scam me with the ''The Bait-and-Switch Refund'' method.

I sold a Surface tablet on November 2nd. The buyer immediately asked me that she wanted the item quickly because it was going to be a gift for her daughter, so I shipped the item as soon as possible.

It took 3 days when the buyer received the tablet, once she received it, she opened a “return request” during the first day.

She complained about several facts that are no valid:

1. The tablet had a passcode (all surface needs to have a passcode even when it's fully wiped from the previous owner because it's now linked a local account). I provided her that passcode and was tested.
2. Also about the language configured that was in Spanish, even when my photos in the listing page are shown in Spanish clearly.

During the “return request”, I noticed her attitude a bit rude and in a rush; requesting quickly a return shipping label and also refunding her full credit. But also, a bit contradictory because she was insisting to me to deliver the real password to login (when I already provided her). I preferred to be careful and first receive the tablet before returning it.
Then, I accepted the returning even when my listing page shows NO RETURNS and it was not a problem with hardware related with the tablet, so I apologized with the buyer and sent a pre-paid shipping label for returning. Today, once I received the tablet, I noticed that she
didn't include the Wall AC Charger. That fact made me suspect her, so I figured out to find another wall charger to test the tablet immediately but unfortunately it didn’t work.

The tablet that the buyer returned to me is not functional (the screen doesn't turn on neither the keyboard), she exchanged the tablet by another one. I could recognize it because inspecting visually the tablet, this one doesn't have a small spot and colorless on the corner of
the tablet.