I have read about it before and the reason why sometimes both buy and sell rates in India is 5-10% higher than original price of Bitcoin is due to high demand inside their country when the price drops and Bitcoins seller like Zebpay don't want to sell it cheap. But sometimes both buy and sell rates in India is lower than the international rates but this also happens in international markets sometimes and all exchanges have different rates on Bitcoin price.
Zebpay only buy and sell inside India this is their explanation about this: https://blog.zebpay.com/why-are-indian-bitcoin-prices-higher-than-international-prices-45cf708b6b1d