Buy 3 - get 1 free..
OP wanted to know if "get" and "buy" can be used interchangeably.
I would like to buy a pack of gum / bag of chips / soda / hamburger etc.
I would like to get a pack of gum / bag of chips / soda / hamburger etc.
Dictionary meaning.
Let's examine what the Cambridge Dictionary says.
to buy something
These words mean to get something in exchange for money.
The most common word for this is buy, which can be used in most situations. Get is another common word that can be used instead of buy.
I need to buy some new shoes.
I need to go to the supermarket and get some bread.
So the answer to OP's query is - Yes. Get can be used in place of buy.
Are "get" and "buy" interchangeable?.
"Interchangeable" also means that "buy" can be used in place of "get.".
Although it is obvious that you are using "get" to mean "buy," this does not necessarily imply that you paid for it.
For example:
Buy 3 - get 1 free..
A clothing store in our town occasionally runs a promotion on ready-made shirts in this manner. It means you have to pay for three shirts but get the fourth for free. (Get four shirts for the price of three).
The word "get" can be interpreted in a variety of ways.
Consider the following two sentences:
1."I will get you a sandwich.".
The sentence could be spoken:
i)by someone who wants to purchase a sandwich for a colleague.
ii)a wife who is going to prepare a sandwich for her husband.
2."I got the iPhone from the Apple store.".
This might be a statement
I)from a genuine buyer
ii)a shoplifter who took it without paying.