Yes. But it depends. The rule of thumb is:
The higher the demand for a book, the more copies you should buy.
It's always better to "go wide rather than deep" (buy many different books rather than many copies of one book). That way you don't get stuck with tons of copies of a book if the price drops, or the market for that book shifts in some other way.
But when a book is in high demand and it's a great deal, there's no reason not to buy multiples.
Here's some examples
So a book is ranked better than 30,000. It might be smart to buy 5 or more copies of a profitable book.
Now let's say that same book is only ranked 500,000. You might only want to buy 2 copies.
The higher the demand, the more copies it makes sense to buy.
- Peter