Hey -
You are getting some GREAT advice and I want to throw in my two cents as well. First of all, if possible, you may want to wait for your Dad to come back into the country - it sounds like he is a great negotiator. Here are some thoughts I have:
1. As someone else already said, try to sell your car first, if you can. Cash is better and if your car is in decent shape, you will be able to get more money by selling it to someone rather than through the dealer. You can use Kelly Blue Book to find out the current value of your car (online).
2. If you do decide to trade your car into the dealer, don't EVEN talk about the trade in until after you negotiate the price of the car you are purchasing (say you are not going to trade it in).
3. I have heard a commercial lately from Autotrader that says they buy cars - they give you a value of your car that they will pay that you can carry with you to the dealership. If you negotiate a trade in value that is better, that is fine, but you have this offer in your back pocket.
4. Look on Autotrader for a car you might want to buy. You can buy a great used car on autotrader. I recently sold a car on autotrader for an excellent price - the buyers got a great deal. But, I wanted to sell it so that I could buy a used minivan. I wanted to pay cash for the minivan, so I wanted to sell my car first. So, there are great deals on autotrader. Often Autotrader will post a link to a carfax report so that you can pull up the vin number in carfax and see if the car has been wrecked or whatever. You can purchase a membership to carfax for a reasonable amount of money where you can look at as many vin numbers as you want in a month's time period.
3. One mistake I made on my first car purchase was that I negotiated the price of the trade in first and then the price of the car. The trade price negotiated was $2000.00. As the car salesman was writing up the sales ticket, he talked out loud and said what the price of the car was, etc. and then he mumbled that the trade in was $1500.00. I spoke up right then and said that we had agreed on $2000.00. And, he corrected it. But, if I had not spoken up, he would have just written $1500.00 in. Honestly, if that happened today, I would walk away from that dealer right then and there. But, I was about 23 then and didn't really know the rules of the game.
4. As others have said - you are negotiating the price of the car. Definitely get pre-approved for a loan by a bank. You can often get a better interest rate at the bank. Then, you just tell the dealer that you do not need their financing. OR, they might offer you a better rate than the bank and you can take their financing. But, as someone else said - do your homework. DON'T negotiate the price of the monthly payment - only negotiate the price of the car. They sell a little book in the store that goes over interest rates and payments - you can even take that book in with you and if you settle on $10,000 car at 5.00%, you can look in the book and see what the monthly payment would be. Or, if you don't want to be obvious about it, there is probably an ap you could download that would do the same thing and you could just look it up on your phone.
5. Definitely shop around. One dealer may give you a better deal on the same car than another dealer will. I had a dealer say to me once - what would it take for me to get you to NOT leave the lot and buy this car? I left the lot anyway because I was just starting my search and so I didn't know what I wanted to pay yet.
6. Please do consider buying used (even if you buy from a dealer). The most value on a new car is lost the second you drive it off the lot. I read an article recently that said the best value in a car is one that is three years old. Personally, I try to get a car that has around 50,000 to 80,000 miles on it - I figure it will easily go to 200,000 miles and then, because it is older, I can usually pay cash for it.
7. Like your dad did, I had a friend negotiate a car for me once (I had totaled my car in an accident and I was driving to the lots in a rental car - they were swarming me and I KNEW I wasn't going to get a good deal). The car I bought was used and listed on the lot at $17,000. My friend negotiated it to $10,000 (I know I would NEVER have gotten it that low). But, the car I bought was a Honda Accord and my friend drove a Honda Civic. He said that we were going to get married and after we got married, he was going to come back and trade his civic in for another/differnet Honda. He basically just played hte game and lied through his teeth. The salesman thought he was going to end up with two car sales and so he gave us (me) a great deal.
8. Also, go to the car manufacturer's website. Several years ago, I wanted to buy a specific vehicle and the website was offering a certain finance rate (better than the bank). But, when I went in to buy it, the dealership offered me a rate higher than what the website said it should be. I told them that the website was saying that the rate was X. They went in the back and did their research and came back and offered me that rate.
Good luck!
L.