He needs to report the income to the IRS for sure.

He will only need to report the income if he made more income then which was allowed for his household size and when his checking/savings account exceeds $2,000.

Say if his household has 3, his two sons and himself and the state allows an income of $1,600 a month for a household of 3 and he sold two cars that month with a profit of $2,000 then he would have to report that income.

If he sold 2 cars that month and only made $1,599.99 profit, then he wouldn't have to report it.

But once his checking or savings reached $2,000 , he would have to report that.