A person introduced himself as a leader ... how do we check the claim for leadership?

Any prudent follower or a leader can easily figure out another leader during the preliminary discussion between each other.

First we need to check his professional background, industries or companies he worked for, his confidence, certificates or rewards that he/she achieved in his/her lifetime, very creative minded and innovative in group discussion. I don't think qualification is required for leadership skills. people management. time management and business continuity plan should have to be there in leaders mind.

One who accept responsibilities and accountability, who understand the environmental factors with in the society and community.

If he or she will be the choice of the majority, one who can change a person to become successful in his life and can answer all the question you ask.