Hi Preben and welcome to the forum,
It kind of depends on what type of supply source you are using really. For example, saying that iPhones are a hot selling item is no great surprise, but that' a tank with some big sharks swimming in it, so you can't even think of competing with a dropship model because you would have no chance.
So you really have to work out what supply chain you are going to follow and then research your market from there.
Cheers