I have developed one app in which i have used the Google Place API. This is what places doc says about limitation.
The Google Places API has the following query limits:
Users with an API key are allowed 1 000 requests per 24 hour period.
Users who have also verified their identity through the APIs console are allowed 100 000 requests per 24 hour period. A credit card is required for verification, by enabling billing in the console. Your card will not be charged for use of the Places API.
So my question is that if i enable billing for Place API then its free? Is it really true?
Yes, you will have what they are saying. I have done that, so I can confirm... If you put your credit card info, you are letting them know that you are a verified user, and that therefore you won't misuse their services.
And for the second question, we are talking about Google here. It is really true, you won't be charged, they can make money from other sources :)
EDIT:
Actually, if you need more than the "verified" option, it seems you can contact them as stated by Thor Mitchell (Product Manager @Google) in this topic at Quora: Pros and Cons of Places API
"The limits on use (after identity verification) is 100,000 requests per day, and we're happy to talk to developers who need more about their requirements."