The problem with your argument is that neither Sadguru nor Ravi Shankar call themselves Saints. They both call themselves Guru or Teacher. Sadguru qualifies it by calling himself a Yogi.

I don't understand how you can assume stuff like this when it is not even the least bit true. Neither Sadguru nor Ravi Shankar have ever claimed to be a Saint/Sanyasi.

If you are not a Hindu then it is understandable to get confused with these terminologies. So I'll assume you aren't and explain the meanings behind these words in the context of Hinduism.

> Saint like Ramdev has access to hundreds of millions of dollars and thousands of acres of lands. They buy hundreds of acres of lands from government at 75-80% discounts. What kind of austerity and spirituality can they preach?

Now let us address issue of Ramdev as he is a Saint/Sanyasi (in the context of Hinduism). A Sanyasi, in Hinduism, is one who has given up material desires for himself but can be involved in the society he resides in. A Sanyasi is not barred from working towards public good in Hinduism. There are plenty of examples of this in Hindu scriptures:

Lord Krishna is himself referred to in the Mahabharata as the greatest Sanyasi. Wasn't he married? Wasn't he the King of Dwaraka? Did he not fight multiple wars? And was he not himself involved in the Mahabharata war? Why then did he refer to himself as the greatest Sanyasi while narrating the Gita to Arjuna? He was a Sanyasi because even though he was involved in the materialistic life he remained detached from it. Saṃnyāsa is a state of mind that is achieved by being detached mentally from the materialistic life rather than physically.

On the other hand, what you are talking about exists and it has a specific word in Sanskrit: It is called "Vairāgya". Do not confuse Vairāgya with Saṃnyāsa (or Sanyasa).

The biggest problem is that people try to interpret Hindu scriptures through Western concepts and completely misunderstand the true meaning behind those words. Worst yet, if they come from another religion they try to compare and contrast Hinduism with meanings defined in their own Religious texts. It is natural to do so because the human brain always tends to find similarities to familiarise itself with the unknown. If you lookup the meaning of Sanyasi in English the nearest word would be Saint. Lookup meaning of Vairāgyi and it will be Saint as well. Now how is that a fault of Sanskrit if there are not enough English words to express these different words succinctly?

You can learn about the differences between Sanyasi, Guru and Saint here (the top answer explains it really well): https://www.quora.com/What-is-difference-between-Sadhu-Saint...

Sadguru himself explains what the difference is between a Guru and a Saint in English: https://www.youtube.com/watch?v=Deh7k-ohE-I

Now you may have problems with them running a business. However, Hindu scriptures don't prohibit it in any manner. In the Ancient days, Sanyasis themselves ran Universities and took donations (called Guru Dakshina) from Kings and in return imparted education to their heirs. The Vairāgyis, which you were referring to as Saints, were actually few and far between even in those Ancient times.

So no. A Sanyasi is not barred from running a business or holding a political office as long as he does it for the greater good and not for personal benefits. Sanyasis in the past have even taken up weapons to fight and protect people. You can read up on "Nath Siddhas" or "Mahants", who in the 12th Century, fought battles with Mongols and Persian invaders and it continued all the way till the British rule over India until Gandhi started the non-violent movement. If you travel around India, especially in villages in Uttar Pradesh, you'll get to hear stories about these Warrior Saints. Many of these stories remain undocumented to this day and remain as folklore.

Not just that. There are instances of Sanyasis having ruled Kingdoms as well. Vidyaranya was a Saint who was entrusted with ruling the Kingdom of Vijayanagara (present day Hampi, Karnataka, India) during the Navratri festival by the Empire's founders (Harihara Raya I and Bukka Raya I).

Hinduism is pretty vast and intricate with lots of historic events due to it being the oldest surviving religion. Having surface level understanding of it will only take you so far.

> How do you decide if some saint is real saint or just a fraud (in the sense he doesn't mean what he preaches)? What is the test?

A fraud is one who misinterprets and misrepresents scriptures. It is as simple as that. Ram Rahim, Osho and Asharam fall in that category. They exploit by twisting the meaning in scriptures to their advantage. The test is quite simple: you have public access to Hindu scriptures. Just check if what they claim can be validated against the scriptures. If they can't then obviously they are twisting it for their own gains. It is as simple as that.

Frauds exist in all Religions. Some frauds do it for illicit gains, some for meeting political objectives, some for forced conversions and some for terrorism. The fault lies with the people who support them blindly without comparing and contrasting with their own scriptures. A majority of the time it is blind following rather than conscious reasoning that is the cause for all such issues.