I posted about this marketplace scam a few months back in the threads for scams on GN.
How it works for the gullible is that they scammer says they wish to purchase the item for whatever price it is being advertised for and they will arrange with a courier company to collect it and to bring with them the purchase price in cash.
This should warn anyone that this is a scam. No courier company will collect unpacked items and most definitely NOT have to their drivers carrying cash to hand over.
If you do agree to go along this route the next stage is that they will apologise and say that the Courier company requires an insurance payment (IN ADVANCE) for carrying cash, and YOU need to pay this now and the purchaser will include this extra amount in that cash payment.
So there you are........the insurance cost is usually around the same amount as whatever it is you wish to sell.
When you cancel the whole transaction, these scammer try on the next stage and message you to say that they have made these arrangements and you are therefore responsible for the cancellation charges, and legal action will be taken against you for this money. Just delete and block
I do use marketplace a lot. Usually with great satisfaction both on my part as a seller and on the part of people getting a nice item for a small cost. I always ask for cash and collection.
Obviously the above scam works on a number of people otherwise the scammers would no continue to use it. It has been around for some years, also on ebay.