I want to buy a dairy cow

Yes, for dairy you should look for Sahiwal, Gir, HF cross, or Jersey cross. Before paying, milk the cow in your presence, do a CMT test on all four quarters, ask which month of lactation she is in, and check age, body condition, and vaccination record. If you want fifteen litres or more consistently, one cow is not enough because peak yield is only in months two to three; you need two cows with staggered calvings. For any cow above fifty thousand rupees, take a Pashumitra or registered vet with you before payment.