Most of the scams would be done and gone if everybody agreed that to sell in the PX you have to be willing to do a video chat on one of the main services (skype, signal, facetime, element, zoom etc) with the buyer & seller.
Yes, I know technology is hard is the excuse folks use.
It's very hard to convincingly fake a video chat. Do a video chat with the seller & buyer and talk and inspect the item over video with the seller holding it and all that stuff. Confirm all details and payments verbally during the video chat, that they match any written communications.
While not fool proof, it pretty much guarantees that the person selling the item actually has the item in their possession, and you can get a general feel for their character most of the time.
For sellers, also you can ask the buyer to go outside and chat in front of their house / work etc or whatever address you are shipping to and then you'll be able to confirm with a google / bing street view that that looks like the address in most cases, as well as getting an idea from the chat if it looks like you are selling to a legit person and not some 3rd party scam drop artist.
Skype will run on most platforms including PCs and Macs and Linux, as will Signal as will Element. If you both have iPhones, then use FaceTime.
Just about every cheap junky old android or iphone has a webcam and can do video conferencing, as do most tablets.
For your PC or laptop if it doesn't have a camera, well that's $30 one time purchase for a webcam with microphone.
If the above became a rather hard fast rule, for anyone you didn't already know well and have verified dealings to all the same address / etc things with, most of the scam things would fade away because it's a lot more work. It's not totally fool proof, but it makes the bar for scammers rather high.
