S&P - hope this doesn't confuse you further, but in the Thirties the Austin agents rarely changed - why would they when they were onto a good thing with Sevens? Can't help for certain about 1936, but in late 1933 the Austin Motor Co's list of Austin agents have (amongst 90 for the entire London area !!) two
shown for Golders Green, neither of them Hertz. They were :
The Newnham Motor Co, 1 & 2 Willifield Pde, Golders Green NW11
H.A. Saunders, 17, 18, 19 The Broadwalk, Golders Green NW11
No mention of Hertz anywhere amongst those Agents listed under London area.
Perhaps the above two may be worth looking into, concerning your Ruby? Or are you sure the car was sold in Golders Green?
Good Luck with your searching. Cheers, Bill

Location: Euroa, Australia

Hi Bill, and thanks Stuart

Location: Windy Swansea

As Bill says, there were around ninety dealers in London but only three were one hundred percentage Austin Dealers. viz: Great Northern Motors in Finchley, H.A.Saunders in Golder's Green and The Car Mart with seven premises, two in both Euston Road and Uxbridge Road and one each in Upper Montague Street, Park Lane and Lancaster Road.
I can confirm that Hirst's Motors of Golders Green were Austin dealers at this time.

Reference: Austin Dealers in the UK. Publication No: 1388

Location: Melton Mowbray

Thanks all. very helpful,interesting too read and look at the old garage photos.

Location: Windy Swansea