I never had a problem selling, however I did learn to never ever use Parcel Post. They have no deadline for PP and do not have to deliver it if they don't have room, etc. A camera I sent sat in a post office for 3 weeks until the buyer went to to post office to file a complaint and they said well, here is...

Buying... Only burned once. Some idiot sold a camera lens stating it was like new, when it was badly hacked, looking like someone did a failed homemade repair job. It even had little sheet metal screws holding it together. The seller said he would refund, then cancelled his account after the Paypal dispute deadline passed. They guy copied his text from another auction and I smelled something before the auction ended. I have bailed out of gone-stinky auctions since.

I've bought a $10000 motorcycle with no issues, sold/bought guitars without incident.