Importing Shortwave Radio from Hong Kong

Hello everyone,

I cam across  this forum  while searching for some related information on Import duty. And since I didn't found it anywhere, I thought to write you all here. I need to some a few things from you, I would be obliged if ever you reply. 

What I want to know is , if I import a Shortwave Radio Receiver from outside of India, and pay it through Paypal at the Ebay international site, then how and at what stage am I going to pay the import duty, since the seller is already getting paid by me along with the shipping charge before he even shipping the material from their country.

Also, is there any way of determining the import duty that I have to pay if I import a shortwave receiver from some International seller ? If so, then can you please let me know, how can I calculate the duty on a 50$ Degen 1103 Radio Receiver from Hong Kong ?

Thanking you in advance and hoping to hear from you soon
Paul