This was not a security deposit, this is a down payment. I was just about to sign the contract. But, for personal reason which I disclosed to the dealership I didn't and they didn't say anything to fact that they would keep my down payment of 10k, or penalize me for not signing the contract. There is difference between a down payment and security deposit?
Yes, there is a difference.
A down payment means you are buying the car, you've made the first payment and you owe the balance to complete the deal.
A deposit is ONLY refundable if you have something in writing that says it's refundable.
You don't have to sign a contract to have a contract. The written contract is only the formality memorializing the agreement to buy the car. You already had a contract to buy the car when you sent the money ($10,000 if I'm reading the paragraph correctly) and you breached it by not buying the car. The dealer is the aggrieved party, not you.
The only thing in your favor is that the dealer cannot profit from your breach.
If the purchase price of the car was $50,000 and he resells it for $50,000 then he is made whole and you're entitled to your $10,000 back.
However, if he can only sell it for $45,000 through no fault of his own, you'd only be entitled to $5000 back.
If he can only sell it for $40,000 through no fault of his own, you would get nothing back.
Those examples are overly simplified and could have adjustments based on any additional expenses the dealer might have in reselling the car and/or the money he pays for the further extension of his floor plan.
For you to get anything back you would have to wait for the car to be sold and determine the selling price in order to determine what you get back.