Income tax for grandfather savings acc

Hello All,

I've been selling few stuffs online using eBay, Shopclues etc( I'm purchasing & selling items without bill ) & I'm using my grandfather's Savings Bank account who is supersenior citizen, He is receiving pension from Gov using other bank where yearly income is below 1 lakh so he is not applicable to pay income tax
Since I'm using his other bank account without PAN card the transcations have gone more than 30 lakhs with mere credits & debits
Advice whether my grandfather is applicable for income tax ?? And how to show the remittance for the same

Thanks in advance gurujis !!