I just went through this. I forgot to go to the post office to drop off a package, and since it was larger I couldn't put it in my mail box. So the next Monday was a holiday, so it went out on Tuesday.
On Wednesday the buyer filed a dispute with paypal. I explained and gave them the tracking information and they said Thanks! The package delivered on Thursday. I message inside paypal to confirm, and nothing for WEEKS. Keep in mind when they opened the dispute Paypal deducted the money from my account. The day before I loose out all together I escalate to a claim. Paypal does there thing. I submit the data, but apparently Paypal doesn't even look at the information in their own system because they found in her favor, and gave her all the money back.
I send a message to the buyer, and she says "Oh I didn't know I had to do anything" I appeal the decision, and this time print and scan and upload ALL the documents rather than use their system. Now the find in my favor. However they refuse to reverse the automatic deduction from my account, so I had to contact the buyer again to pay me again. Meaning paypal deducted fees TWICE. All of this over $12.
It was the principle of the matter to keep my recently opened account in good standing, and not really about the money or the fact that the item had not been used in YEARS!