Well the Exit Polls conducted by news channels and other agencies are a mixture of the survey opinions of people (the number of people may vary from less than 100 to 100,000+), past trends, recent events, etc.....so there is some reality in them. This "some reality" may differ from agency to agency.
The main thing is that these exit polls can be almost right on a National Basis but these exit polls can not trace regional dynamics of different parts of India.....I noticed this in last 3 Lok Sabha elections from Bihar to Tamilnadu.