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I bought a 35f1.4l from adorama and found it to be not tack sharp. Sent it back and got a second. Still not sharp. ...I rented one from lensprotogo and that was extremely tack sharp.
Because of the very narrow depth of field at f/1.4, fast lenses are very sensitive to manufacturing tolerances. If two out of three lenses weren't sharp, it may be that the combination of tolerances in the lens and the camera are adding up to an out of range total.
If that's the case, having the camera and lens calibrated by a Canon service center may help.