Making believe is when you pretend.
This idiom means: you are ready to fight with energy and determination for what you believe in.
If you "don't buy" something, that means you don't believe it. You're saying you don't believe someone's explanation.
"Believe it."
I believe the idiom you're looking for is "You can't trust a person further than you can throw them". The meaning is meant that you cannot trust someone because you can't throw them very far.
It is said about person or a business and it means dishonest and only interested in making money quickly
Nothing. I believe you mean to run out of STEAM, which means that your "engine" doesn't have any "steam" in it - you've run out of energy or drive for something.
It's not really an idiom. It means "what are you thinking about."
RFP is not an idiom. It's an abbreviation.
It is not an idiom, it means your nose is itching.
idiom
Nothing. I believe you misspelled WORLD - "on top of the world" means that everything is going well for you and you feel great.
To take something that someone says with a grain of salt means that you should not necessarily believe everything he/she tells you.