1. The appropriateness of working in a leather shop can be related to its inherent wrong-doing of killing animals etc… In the Bhagavad Gita Lord Shri Krishna calls upon us to do our duty to the best of our ability, with detachment and to surrender our actions unto Him. Your question can be answered in the same manner. Whether it is a leather shop or a place where missiles are being manufactured to kill others, if we work with detachment, then the effect of karma is reduced or mitigated.
However if the seeker is a staunch believer of non-violence that he/she cannot tolerate the sight of leather then he/she should quit immediately, which takes us to the second question.
2. If one does not have the courage to live up to and act upon one’s convictions then it creates a dicotomy within oursleves.
Unless one is daring in life, one should not attempt to take up ambitious projects. Fearlessness is a sign of self-confidence and total faith in the Lord.The choice is ours – stay put in the job and work with detachment OR leave and move to something more fulfilling and rewarding to the Self.