To Have an Axe to Grind
Hacer la barba
This expression is used to say that someone is using flattery or tricks in order to take advantage of someone else. So, this trickery person has a secret selfish purpose that he/she will get by means of adulation.
In the 1800’s, a story was published. In it, there was a boy who was an excellent ax grinder. Then, someone arrived with an ax for him to grind. The ax was heavy and grinding it represented a hard work to do. The man convinced the boy by telling him that he was the best, smartest, strongest ax grinder ever. In the end, the man didn’t pay or even thank the boy for his work. We use the negative form of this expression to mean that we are honest, unselfish people.