I think it's more like convincing people to buy a solution for a problem they did not know they had.

That does require the initial premise that the underlying product is actually a solution, which isn’t necessarily true. Marketing’s just a tool that can be applied.

If one was marketing something like a scam or even just something useless, for instance, I’d say it’s still marketing even though there’s no solution present.

Of course, under that same reasoning, “manipulation of people for gain” also isn’t necessarily accurate.