Can I get my money back?(used car) ?

Yes as they have to clean the car anyways, however the salesman wants to sell you a car(as commission is his wages) so won't mind if you decide to buy a different car on their lot as the salesman still makes his buck.    If you want to go elsewhere, then they will complain but life is full of changes.  You have not taken delivery on the car yet so they have to undo the paperwork....you can string them a line like "I am under investigation for stealing cars from car lots with fake money"  Maybe THAT IS TO OBVIOUS?  You can lie your way out of it if you try.  They lied their way into selling you the car (it is not lying if they just don't inform you about anything)

Mommy won't let me have it; the money is for college.

or 

My ex is seeking "child support" and has gotten that OK from the judge.   That means I can't afford a car right now.

Or some lie you can imagine to I got the carfax on this car and it is a PoS.

Please don't make any decisions because on a carfax report.  They are often incorrect.

You will have to review the contract you signed to determine if you are able to back-out of the deal. 

The worst thing you did was not get it checked by a mechanic first.  If the car comes with a short term warranty, make sure you get the mechanic to check it asap

Not likely. If you back put of the deal, you could lose the money you've paid. Ultimately, it depends on what you may have signed.

You should never put more then $100 down on a car deal. You're about to find out if you're dealing with a fair used car salesman or a shrewd lowlife POS. 

Of course you won't get your money back. If it test drove OK it's probably a good car. So pay the balance and stop worrying.

Read the sales contract.  But do not believe so much on carfax reports.  If the car test drove fine, the car might be ok.  I drove a used car with 11 red flags for over 100k miles.

You've signed a contract to buy the car. There will be something in the contract about the penalties for breaking it. You might be able to get some of the money back but not all of it. That's why you read everything before you sign anything, including the contract you're signing and the vehicle report. 

Read your contract.  If it says the deposit is 'nonrefundable', you maybe in trouble.  This is something for your local lawyer to look at, not Yahoo Answers.

a) You should have checked the Car Fax FIRST  before handing over any money. Fail.

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b) Buying a car with your eyes based on appearance is the wrong way to go about evaluating a car. Fail again. 

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c) It doesn't matter if it's your first time, you could have done a lot of preliminary research and asked advice about buying a used car. Another fail

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d) Finally, we cannot tell you because we do not kinow what you signed, and if it was a purchase contract, exactly what the terms and allowances are in it. Not reading all the fine print and knowing exactly what you were getting into was an EPIC FAIL.

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i HOPE IT TURNS OUT ALL RIGHT FOR YOU. GOOD LUCK.