There is a lot in FB that selling item below market price. For example, a Shimano fishing reel where is standard market price is RM500+ is selling at 200+. Scammer in order to persuade buyer is giving COD option. But this COD option itself is a trap because the seller is using 3rd party courier.

From this, U actually no able to open the package to check because the moment U open it, it consider sold even the item is not the genuine product.

U either ask courier can check the item before paying or not only (which 3rd party courier doesn't let U to open it without paying first)

If U see item below market price on FB. U can troll back the seller by order it then cancel the order afterward. Let them bare back the deliver cost

Not sure. I don't think there is any courier that can let U to open and check first.

Because if the package/seal has been opened. It could cause dispute and the sender could claim the courier make changes to the item inside.