Green’s Dictionary of Slang

ten-per-cent adj.

[ten-per-center n. (2)]

inadequate, useless.

[US]J.T. Farrell ‘Patsy Gilbride’ in To Whom It May Concern 43: There was nothing for me in that town full of ten-per-cent chiselers.
[Aus]T. Ronan Packhorse and Pearling Boat 164: Those ‘Foreshore Rats’, those ‘ten-per-cent Pearlers.’.