Potential Tax Liability

I have a friend who inherited many electronic items including those of the audiophile variety. Through ads on this site and others, he sold about $60k worth of equipment within this year.   He is not a dealer and does not have a business, either physically or on paper.  Most of the payment transactions were made through PayPal. He is now worried about potential tax liability. Sometimes he created invoices. Sometimes the money was sent through PayPal's "Friends and Family" option. The money was transferred from PayPal to his bank account periodically. It suddenly occurred to him about possibly having a tax liability.    Made me curious too.   Would these proceeds need to be declared as income to the IRS?