Torque sign follows your rotation convention
The mistake
Flipping torque signs because a force points down or left, rather than because of its rotational tendency.
Why it feels right
Force signs are tied to direction, so torque signs get treated the same way.
How to catch it
Downward forces sometimes get positive and sometimes negative torque in the same equation.
The first principle
Choose clockwise or counterclockwise positive. Each torque sign depends on which way that force tends to rotate the object about the axis.
A downward force on the right end of a beam about a center pivot produces which sign if counterclockwise is positive?
Common wrong move
Positive because down is chosen positive.
Correct
Negative; it tends to rotate clockwise.
Make a fresh prediction before referring to the worked example.