In some regions in India, people do not buy salt on Saturday. This is not based on any scripture in Hinduism but it is based on oral tradition. Again, the not buying salt tradition is restricted to few communities and few regions. It is not pan India or pan Hindu belief.
Some people associate salt with Shani Bhagavan. This is the main reason why salt is not bought on Saturday.
It is believed that buying salt on Saturday will result in money related problems. There will be unexpected financial crisis and there will be debt.
Donating already bought salt on Saturday is considered beneficial.
All these practices are strictly followed by people who believe strongly in astrology and horoscope.
How Far Is This True?
People always look for excuses for failures in life. No one wants to take up the blame for failure. This is the main reason behind such beliefs.
What makes such beliefs gather strength is fear and lack of proper understanding of Hindu religious teachings.
Such believes are going for thousands of years. Some believes change or take different form over a period of time.