As a tourist, I got a lot of hassle in India from rickshaw drivers, shopkeepers, hotel owners and general touts. The best thing I ever did was to learn to say 'I don't want it', 'Go away' and 'That's too expensive' in Hindi. It makes people stop hassling you faster than anything you could say in English, possibly because it shows that you're not a brand-new arrival to India. Also good is to learn 'my name is...' which gets a great response from local people rather than just replying in English.
Get a phrase book or (better) get someone to teach you when you arrive.
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