I think the article's original title should stand. While some people might consider it "baity", I would describe "Smartphones Are Spies" as an accurate description of reality and the content of the article.

The article is making an a public accusation: a lot of spying is happening, and they are naming some of the (in their opinion) responsible parties. Changing that to a title that only indicates the general subject of the discussion ("location data marketplace") obscures the article's thesis: "Your smartphone is probably sending your precise location to companies right now." (which is just a more detailed way of saying "smartphones are spies")

[regardless, it's your house, use whatever titles you want]