Green’s Dictionary of Slang

blind Freddie n.

also blind Freddy, blind Freddy’s dog
[the blind beggar Frederick Solomons (d. 1933), known as ‘Blind Freddie’ who frequented the Sydney streets in the early 20C]

[1910s+] (Aus.) an imaginary figure seen as representing the lowest denominator of incompetence; thus used in phrs. such as blind Freddie could see that, wouldn’t fool blind Freddie.