Who is Satya Sai Baba? Is he a Bhagavan as people call him?
We are not familiar with his teachings to comment on his identity. Srimad Bhagavatam, Bhagavad Gita mention the characteristics of an authorized incarnation. There are auspicious markings on the Lotus feet. The advent of the particular incarnation must be predicted in the scriptures. He must be able to show the universal form which Krishna revealed to Arjuna on the battlefield of Kurukshetra. He must perform extraordinary activities and not just perform some magic tricks. The purpose of the particular incarnation is also revealed in the scriptures. There are many other indications also. Only if these conditions are satisfied, we can accept somebody to be an incarnation.
There are also many references in the scriptures, of people having a few siddhis, who falsely claim to be God to cheat the innocent public. We must guard against this phenomenon which is unfortunately quite prevalent in India.