Beautiful find! My dad and grandfather had that same hifi. Beautiful system that sounded great. I do remember that they truly did not like short curcuits on speaker output.
In such a case I would ask for a holding deposit to secure the item. If not paid for and collected within a specified time they lose their deposit and it goes back on sale.
Supersonic did make Hifi systems such as the quality Supersonic One-Eleven. It had some wonderful speakers and had Garrard Turntables. You had a AM/FM tuner where you could preset FM stations.