Is this a scam? Yahoo Finance?

Yes its a scam and a bad one at that. Yahoo Finance is only so you can track the performance of the stocks. I used it to communicate with my broker but it isnt possible to make transactions on it. Never agree to buy anything that you cant see or touch in person. It was good of you to ask someone about this before going through with it. I would suggest getting a small compact car that is cheap on gas and insurance for your first car rather then something like a Mercedes that is a pain on your wallet if it breaks down. Look on Auto trader or a website like that and you will find a good deal, also avoid dealers as that is a whole scam in itself. Good Luck!!