Replying to [Firo]:
you need to have a wide know how of products and about the market in those area's, if you see new products and designs made in some factories you can see if these would fit into the market and hit good sales, sure you can use companies to tell you this information but if you have the eye and the background you know.
Not all products i have bought have been great sellers, but each time we learn, in most times you would see what you feel can be a great seller while on your visits or travel, keep you eyes open, if the end customer as a need for a product they would buy it.