Apparently, he wasn't that confident about AC/DC, because he was 32 and, quote, "an oldfart." Plus, the Hoover gig paid around 700 bucks.
But his audition blew the band away, and he was announced as their new lead singer on April 1st, 1980. That same month, his Hoover commercial aired. And to this day, no vacuum cleaner has risen to that level of coolness again.