I don't believe all.
>> I don't believe at all.

but , I believe it just a little that they told me.

>>However, I do believe a little bit of what they tell me if I ask how much the cost of an item on sale.

They sometime lie to us for sale

>> They sometimes lie to us.

I think my responsibility, if i purchase something
I want to be smart consumer.

>> I should be responsible and be a smart consumer or customer when I purchase things.

That'why There are many thing in the world what i want to buy.

>> There are many things in the world that I want to buy.