Get $1 stuff for free plus extra $1

I know this title sounds ridiculous but believe me,this will twist your mind for the second time.

If you have learnt complex number,you should know that i²= −1,where i=(-1)^½.
And i is an imaginary number.

So let's start with 1.

1=(1)^½
=([-1][-1])^½
=(-1)^½ x (-1)^½ From i=(-1)^½,
=i x i
=i²
=-1

So, 1=-1.

Now,write this down on a piece of paper,go to the nearest mart,get $1 stuff for free and ask the shopkeeper for extra $1