Hello,
Is very simple. You can pay with any master or visa credit card (Amex not accepted).
You do not need to open an account with paisapay.
You can use you ebay (us) account to make a purchase, just ensure that you change the shipping address before making the purchase.
For Paisapay simply enter your cc details to make the payment, no need to open an account with PaisaPay.
Many Indian sellers also accept PayPal, you can ask the seller before making the payment.
Regards,
Devesh