General advice:
If a listing is too good to be true -- such as a new item that is selling for a fraction of its retail cost -- that is certainly a warning sign. And if a relatively new seller is suddenly selling thousands of dollars worth of multiple quantity listings at fire sale prices with free shipping from overseas with extended handling times and very long shipping estimates, you should be very concerned, particularly if the items are expensive electronics, cameras, musical instruments, tools or outboard motors.
In general, you can avoid a lot of headaches by choosing to purchase only from established sellers that have recent and past positive feedback as a seller for selling items in the same category that you intend to buy. If someone is selling a dozen apple watches, but has no feedback, or only has feedback as a buyer, or only has feedback for selling dress patterns or fishing lures (actual examples I have seen), perhaps wait until they have a track record of positive feedback for selling electronics before you buy from them.
You might miss out on a good deal from a new seller once in a while, and nothing can guarantee that you won't still run into a scammer anyway, but you can avoid a lot of potential problems by following that advice. Anyone can put together a listing that looks nice -- it is not hard at all to simply copy an existing listing -- but it is much harder to create a history of consistent sales and positive feedback.
