Gethin joined the family owned Stadium Garage (the Toyota Specialist and KIA Dealership of Skewen) in 1953. With the exception of two years National Service in the mid-fifties, he has remained with the business throughout this time. Whilst with Stadium, he has worked in every section of the business, and in the process, gained extensive knowledge of the motor trade and project management.

Over the years, he has become involved with various local and national organisations whose role is in the economic development of the area and in training and education issues concerning the motor industry. He is currently the Chairman of the Federation of Small Businesses (South Wales) and Chairman of the Retail Motor Industry Federation for South Wales and the West Country. He also represents the South Wales Area on the National Board of the RMI.