I do not understand this situation 
For now, I believe that I can just fly to India and buy a lot of Bitcoins for the very low price (20% cheaper than regular price)? Am I right? And than sell for EUR or USD and earn 20% ?
Preev says 1 BTC = 25340 INR
Unocoin says buy 1 BTC = 21032 INR
Can someone explain it to me?
Your math is correct. But from what I know, none of the exchanges or trading platforms will let you buy bitcoin for cash. All of them need KYC docs. Unocoin need you to be Indian resident with Indian address proof and Indian bank account to buy bitcoin from us. So it is not that simple. For now, I believe that I can just fly to India and buy a lot of Bitcoins for the very low price (20% cheaper than regular price)? Am I right? And than sell for EUR or USD and earn 20% ?
Preev says 1 BTC = 25340 INR
Unocoin says buy 1 BTC = 21032 INR
Can someone explain it to me?
If you are a verified customer, then yes we sell our bitcoin to you for just 21032 INR
You can buy 10 btc per day from us.