Character is best demonstrated over time.
If a random stranger walks out of the wilderness and starts giving advice, you will wonder who they are and what they're up to.
But if an established member of your community, who has done all sorts of great things over many years and who has shown good judgment and care for others, starts sharing opinions, a lot of people will listen to them.
That's why professional persuaders put so much effort into establishing their own characters and brands: they know it takes time.