Lord Shanidev is the Lord of Saturday. Most people have a misconception about Lord Shanidev that He is very cruel and pitiless. However nothing could be further from the truth. It is so that Lord Shanidev has been assigned the task of delivering justice to the jivas as per their karmas.
Now the jivas do not think twice before committing any karmas and later on when the time for repayment comes, they start to blame Lord Shanidev about being heartless. The fact of the matter is that He is a very just Deity and always does what is right.
Here is a list of 8 items which you should avoid to buy on a saturday if possible. However it must also be noted that it is a generic guide and may not be applicable to everyone and anyone. For your individual horoscope you should consult an authoritative Panditji or astrologer who can calculate the exact position of your individual planets before suggesting anything.
However there is nothing wrong in being cautious and avoiding to buy such things if it is a Saturday.
A few lines about Lord Shanidev
He is the Lord of Justice, so benevolent and so kind
Yet most of us think He is heartless without soul or mind
If you do good karmas you will receive all His blessings and boon
But if you are on the wrong path, be sure to get retaliation soon
It is not without purpose that nature has given Him the justice seat
You cannot escape Him, if you are a bad person or a cheat
Try to avoid buying these things if it is a Saturday o dear
Consult your astrologer if you want to be more specific and clear
Til, leather, oil, Iron, brooms, black cloth, blankets and coal
The wise say to buy these on Saturday should not be your goal
Yet if it is very necessary, just Pray to the Lord and proceed ahead
Be careful if you have sadesatti/mahadasha, lest later tears you shed