Interest speaks all sorts of tongues, and plays all sorts of parts, even that of disinterestedness.

Self-interest is a fluent actor. It can present itself as principle, as concern for the team, as reluctance, and most convincingly of all as having no stake in the matter. The person doing it is usually not lying; they have persuaded themselves first, which is what makes the performance good. The tell is rarely in the words and usually in the fact that the disinterested advice happens to be the advice that suits them.

When someone insists they have nothing to gain, ask quietly what they would gain if they were right. Run the same question on your own most selfless-sounding position this week, and answer it honestly.