Here are some blunders from my perspective. I'm a power seller on ebay, I mainly sell brand new items given to sponsored athletes by the sponsors. I need to have great feedback because I'm often selling items that are copied and sold on ebay. (knock off sunglasses are the perfect example). I've got to have good feedback so people know they are getting legit original items.
I sold a pair of ski boots to a guy in China. I clearly state in my auction that international shipments are sent using standard air mail and delivery times can vary drastically depending on their countries customs. This guys boots don't show up, so we track them. The tracking info clearly says that it has left the USA and is waiting in China to be delivered (in customs). We email back and forth many times and he finally threatens me with negative feedback unless I give him a refund. I have no power over something that is setting in customs in China, but before I could even reply to this last email I see that he has left me negative. Then THE VERY NEXT DAY he emailed me telling me he got the item. Of course there is no way to remove feedback unless I PAY ebay (through the seller resolution center). Ebay account #1 is ruined, time to start a new account.
I sold a vehicle, a 1970's jeep CJ-5. It had a new motor and new fiberglass body, but otherwise was a 30+ year old jeep. This local guy wants to bid on it, so he comes by and takes it on a 1+ hour test drive with his son. He bids and wins the auction, comes back and before paying takes it on another long test drive. He seems very happy and gives me cash. A full month passes by and this guy calls me saying there are all kinds of problems. He said he took it to a mechanic (first mistake) and the mechanic told him it needed a ton of work. Of course it does, its a 1970's jeep, its a 'project car'! This guy pays $100 to take me to ebay resolution center and then the resolution guy from ebay basically laughs at him on the phone, he test drove the car before he paid, the auction was accurate, so he had no case. He still left me negative feedback. Account #2 down the drain, next...
I sold a mountain bike that is in "excellent mechanical condition, normal signs from being used for over a year". The buyer emails me when he gets the bike saying its scratched. I tell him this normal, but ask what can I do to make the situation better. He says he wants a partial refund of $500 (bike sold for $2000). I tell him no way, I can give him a full refund if he sends the bike back. He says he doesn't want to deal with shipping it, and either wants a partial refund or he will leave neg. Again I say send it back for a full refund (I'll even pay for his return shipping). No reply, negative feedback left later that week. Account #3 done.
I sold a climbing "cam" for over $100. The person says they never got it and want a refund. I track the package and it shows that it was delivered. I email the buyer with the tracking info. The person then changes the story and says they got it, but nothing was inside the package. I tell them it was there responsibility to turn away a package if it looks like it was opened, and I can't do anything on my end, especially after they have changed their story and are obviously trying something. After another 5 emails asking for a partial refund and threatening with negative feedback, he finally negs me. Obviously he was scamming, but ebay has no way to protect the seller. Another account ruined.
Overall I've lost several accounts (over 10) to negative feedback that was not deserved. Ebay has taken away the ability to leave negative feedback as a seller. That means once the auction is over I as the seller have absolutely no leverage on the deal. The buyer can leave negative feedback for no reasons at all and with no worries about my retaliation. In order to get negative feedback even looked at by ebay I have to pay to open a dispute.
Combine that with the new fees, depending on the final price the seller will be paying 15% or more of the final price to ebay and paypal (both owned by the same company).
Anytime you feel like you got screwed over buying something on ebay, log into the ebay forums and look at the hundreds of complaints coming from sellers. Many of the largest powersellers that are selling more than anyone on ebay (and therefor giving ebay more money than anyone) are quitting ebay by the day. It's really sad the way things are going. It used to be a great place to garage sell all your junk or find some cool things to buy, now its turning into another internet cesspool thats full of scams and people getting screwed on both sides of the coin.