The distinction is that if I see a billboard (or magazine ad, or TV commercial) advertising a product I don't think that I have a relationship with the billboard and they know me pretty well and have my best interests at heart... so I don't think that if this particular billboard that knows me so well is promoting a product to me then it must be a pretty good product for me (especially because this billboard doesn't usually go out of their way to recommend products to me).

But if a friend of mine recommends a product to me, well, I do think all of those things.