Sydney builder Bill Issa promised to fix up rundown family homes and transform them into something flashy and new.

"It will feel like a new home," he promised one client. "It will look a million dollars when it is finished."

But when his clients started to complain about the 53-year-old's shoddy work, Issa responded with a series of violent attacks - firebombing homes and offices and beating one client after ambushing him when he got out of a lift.

Issa was convicted last month of arson and attempting to pervert the course of justice in the Sydney Downing Centre District Court. In total, there were six alleged firebomb attacks across Sydney between March and May 2013. Issa was convicted of five.