Oh boy...
My worst experience as a seller:
During my first eBay adventure as a seller I sold an X-Men comicbook lot containing around 100+ books with a good number of key issues, as well as variants, all bagged and boarded and in great condition. I honestly forgot for how much it sold, but I do remember it reached three figures. The meat of the situation was that the buyer, after a week of having received the books opened a dispute with PayPal alleging that books were missing. That, of course, wasn't true, so I countered every one of his arguments and, for a moment, it seemed like everything was going my way, until he was told to return the books in order for me to refund. The story, however, didn't end there because, not only did the seller kept the books he said that I didn't include in the package, he sent the remaining books in a box of BBQ wings without ANY padding. And what's worse, the box still smelled. I pretty much received the majority of the books either bent or warped. I appealed this to PayPal, but nothing came of it. I was livid, so I ended up gifting the books to a friend of mine.
This, being essentially one of my first experiences as a seller, pretty much deterred me from selling on eBay for quite a long time.
And as a buyer:
Two or three years ago I bought a Motoko Kusanagi statue by Union Creative from a Japanese seller. There were at least two US sellers that were selling the same statue, but were asking a lot more for it, so literally importing it seemed far more economic. Also, the added benefit was that the Japanese seller was selling it new. Long story short, it arrived moderately fast, but I was surprised to find that the statue wasn't in the box, and that instead of it the box was filled with paper towels...a whole bunch of them. I was duped, it seemed, so I contacted the seller on the spot. Communicating with this seller was a bit of a struggle, though since he wasn't fluent in English, so I was essentially writing short sentences so that he could understand. Thing is I ended up filing a dispute with eBay and lost, even with proper evidence. Then went to PayPal and, again, after a lengthy dispute, lost. Even after all of this, I kept going back and forth with the seller through DMs, but it went nowhere. Fast forward a month or so after all of this took place, and the seller contacts me to explain that, since he has a store, the box I was sent was for display purposes and that the statue that was supposed to be inside was tucked in another box for safekeeping. He kept saying how he felt "shame" and was extremely apologetic, which I understood. After going back and forth on what to do, we pretty much came to an agreement, and he ended up sending me the statue and refunding me 35% of what I paid, which was a surprise to me because we had talked about a refund, but not for that much. I've come across a lot of honest sellers in my time using eBay, but never one like this one.
I've had other bad experiences, which are the usual many have had before, like stuff I buy being poorly packaged, receiving the opposite of what I paid for, terrible customer service, sellers that think one must ask the condition of an item before buying, etc. But this two I would say are the most...memorable, for lack of a better word.