Once you get paid as a seller, and you ship the item to the buyer and the buyer has a change of heart, or finds some sort of fault, or even pulls a switch-a-roo with the same item they had that was broken, all they have to do is file a claim and the seller is on the hook again for a refund. Basically, the buyer still has you by the balls, even if THEY are the ones that broke the item, etc.
A few years back, I sold a Dell motherboard on ebay. The auction pics showed the screenshot of the BIOS that had the service tag and serial number of the motherboard as well as the picture of the boards serial itself. Buyer gets it, waits 2 weeks and then claims the board is fried and files a claim. PayPal immediately froze my funds. They instructed me to give him a refund once the board came back to me even though I tried over and over to show the PayPal fuckwit the auction pictures of the board actually running in a computer. He let it slip that "maybe the guy had buyers remorse".

I let him have it at that point that I didn't give two shits and a squirt what kind of remorse someone has when they buy on ebay as it stated in my auction that all sales are final. He didn't care about that either because aparently, THEIR policies trump anything I can write in my auction.
I got the board back and looked for the serial and the secret mark I made with the sharpie and sure enough it was the same board. I then put it in the PC case and it fired up perfectly. I called PayPal back and I informed them that the buyer filed a false claim because the motherboard works fine, and their response to that was, "well, you have a good motherboard that you can resell on ebay and the buyer has his money back. You're both good to go"
WTF???
I then RElisted the damn thing again, restipulating my terms and the fact that the sale is final along with more pics of the board running in the computer. I also made sure ALL info was correct for the board right from the Dell website as far as model number, compatibility, etc... The thing sold right away and I shipped it off as soon as I saw the payment in my PayPal account. A week later, I get a message from the buyer saying that the board doesn't work. When I asked him specifically what he was trying to do with it, he told me the parts he was installing and I knew right away that the CPU he was trying to use was NOT compatible with that board, just as my auction said. He filed a claim anyway and once again PayPal froze my account. PayPal once again informed me that I had to take the board back and refund his money because the board wasn't as described. I told the fucktard on the phone that the info I posted on the board was DIRECTLY from the Dell website, so the info was indeed correct. He then said that the info I had on which computer model it came in was not correct as the buyer had stated. The Dell 5100, 5150 and E510 series computers came with a variety of options and there were 10 different processors available. Depending on which CPU you chose, they put in a specific motherboard. I had the exact motherboard part number and the models it came in in the description but stated that the board does NOT work with the Core 2 Duo, which is what the buyer was trying to install. The PayPal guy made reference to the part of the description that I had listed the E510 as one of the models which is what the buyer was going on, thus why I was in the wrong. No matter how well I explained it to the guy, he wouldn't listen.
The buyer again got his money back and I had to AGAIN relist the board and was out shipping for the 2nd time. I informed the guy that next time I get a payment via paypal, I was withdrawing the money and when it hits my bank, I'll ship the item so they can't freeze my money anymore. He then got snippy and saidd that they can FORCE the refund if the need to. I asked him how the hell he was going to do that when all I had to do was call my bank and have them put a hold on ANYTHING PayPal related coming out??? He said they have their was up to and including filing a small claims lawsuit.

Bring it on fuckheads...
So... it goes without saying that they cover the buyer 98% no matter what the seller does or says to protect themselves...
The 3rd time I listed the motherboard, the buyer paid, I withdrew the money and sent the board off 3 days later. He left me positive feedback within 7 days and said it worked perfectly and was exactly as described. What a coincidence....