That's never happening here. We have been doing fine without such a system. Lots of deals happen here every day without any issue. What you need to look for is that the person you are dealing with has a good history on the forum, has dealt with other people before. New members who can't show good history/ratings often offer to ship items before the payment happens in case the buyer has a good rep. If both parties are new and have no history/ratings, most people would advise for 50-50 payment before and after the shipping is done. Or just refrain from buying and selling till you have established a good post history and have made some friends. Members who are very new and are only interested in buying/selling are a huge red flag. If you (I mean anyone reading this) are among them, just stick to OLX or FB marketplace.
Those are good points. I hope this is the case and the seller reverts but all signs point to a scam, I'm afraid. Happy to be proven wrong.