Hang in there. It's not just Posh, such buyers are on many platforms and they are doing it at a pro level. Like half of my sales are by scammers and claimers now, with each order I wonder what's now? Not to mention, I list a detailed description with measurements, pics from every angle and inside, codes and video. Last 4 orders on Posh were like: case for non-existent odor in BNWT $2350 bag (returned worn, stole auth card), case for BNWT bag in box like "everything is flawed" with this bag (return denied), 2 buyers claimed the price they paid was not their offer/wrong charge on their cc (I had to explain that seller doesn't see their cc and doesn't have access to payment processing). Claimer/scammer on Etsy opened case and demanded refund before shipping the return claiming not as described, while I literally circled for her areas at the pics and part of description where it was described in details. It's just January-February sales so far.
On Posh bots seem to approve returns, so you need to respond literally within minutes with your photos and tell your side of the story. I keep uploading videos for them too -- packaging, unboxing returns - like it's my job. Gosh.
ETA: they won't cancel your account, cancellations are not counted against sellers.