The exit poll is definitely more reliable than the pre election surveys because exit polls are conducted across a sample of voters across India when they are exiting the polling booth. Hence the reliability of an exit poll is more than a pre election survey. However, you need to understand that any poll is done on a sample. For example, if the population of India is 130 crore and if there are 50 crore actual voters, then they are evaluated based on a sample of around 20,000 or so voters. That may or may not be entirely reliable and in a complex and diverse country like India, quite often such exit polls turn out to be wrong.

However, these exit polls are often effective to give you a drift of how the election results are likely to be. For the stock markets, these exit polls are an important cue and the rally on Thursday and Friday was largely driven by expectations that a stable government may be formed at the centre. For the final verdict you have to wait for the 23rd May when the actual results will be announced.