In 2000, Hari Sampath, a former security guard at Sathya Sai Baba's ashram - who knew well many of the leading figures in the ashram and the Central Trust, wrote:-
Sathya Sai Baba is a highly intelligent, extremely knowledgeable, and gifted orator. He has the ability to absorb a lot of detail very quickly and assimilate the information. You must remember that although he never attended school beyond the age of 14, he has been constantly meeting with thousands of people from all walks of life, and from these people he observes, and absorbs.
For e.g. he can put carefully worded questions to a cardiologist and from the answers, get a good idea of what is a mistral valve relapse. The next day, he will surprise a group with this specific information and do it in such a way that people think he knows a great deal more than what he actually does, and had known it since he was born. This is, in my opinion, Sai Baba's biggest ability/trick, which he uses extremely well to convey the impression of omnipresence, omniscience etc.
This exactly is what he does in the case of most "omniscience miracles" too.
Regarding the knowledge of Vedas, scholarly abilities, and ability to put things in easy examples, yes, he has all of them. Remember even Ravana, the asura was a master of the four vedas.
Actually, to my mind, Sai Baba is one of the most intelligent and capable persons I had ever come across.
He could have and certainly would have been a huge success as a politician , businessman and world leader had he wanted it.
But, unfortunately, he combined all these three things and added God to it, wanted to be God. He wanted fame, power, glory and the adulation of masses. This was the way he chose to attain it.
He has perverted sexual weaknesses and desires and an ever increasing greed and lust for fame, recognition and power.
How very very sad. Just think what all he could have been, and what he chose to be. I am positive that his life would indeed be a message to mankind, but not in the sense he means it. Instead , it will certainly reflect the great principle that untruth, deceit and adharma, will NEVER win, no matter how many people support it, or whatever resources such an effort has.