Old thread, but I thought I'd post what is close to the last straw for me. It might actually have been the last straw... we'll see.
I encountered a second, in all my years selling, theif.
The first one was clueless, but a thief none the less. This recent one knew exactly what she was doing. She couldn't tell if her device had failed or if the charger for the device had failed. She bought a charger from me for $25 plus $5 shipping, determined her device had failed (still would not charge), so clicked "didn't work", got all her money back. Meanwhile, eBay charged me both ways shipping of $11 plus final value fee of $4.
This, despite having video evidence that I presented to eBay that the item she returned worked fine.
I didn't realize that selling a $25 item (that might net $20 after fees) on eBay is risking a $15 loss. That's a dumb bet to make.
And when you get into items priced higher, the fees get huge; an item selling for $500 would have earned eBay $75. That's too much for me. It used to be that you at least got eyeballs, but lately the number of views has been 0 or low and eBay wants to gouge the seller further by "boosting" your listings.
I think the eBay seller era has passed for me. It was fun while it lasted.