I've had two issues with posh, but overall experience has been great.
One did involve a case.
I sold some Burberry flats which I got as a Christmas present from my brother and his wife. Wrong size, waited too long to return, etc... I am 100% certain they were real.
I shipped when I was supposed to, was notified a few days later buyer was unhappy and PM was "investigating" they never asked me any questions, did any research at all with me and after a couple of days I was notified the shoes were to be returned to me and I wouldn't get the funds. I emailed them a couple of times on how they do their research, authorize a return, etc... They just referred me to links with generic info. Got nowhere with that in other words!
Other than that I've sold quite a bit of stuff through them! Hate that 20% though!
How frustrating! I wish my buyer would have communicated with me before opening a claim. I have no idea what the issue could be. Before accepting her offer I even messaged her to remind her that the watch needs a battery. It's not a large amount of money ($35)... she got an amazing deal on a beautiful watch!