I have been working for many years in the automotive industry and lent and worked with a mandate and you can get a good deal. It takes some time and effort, but basically your retailer wants to trade. You just have to figure out what the bottom is, and it takes some education and negotiation.
First, you really should decide which car you want exactly. Try all the cars you are considering. Once you've found "one", find out what you should expect to pay for it. If you have a car to trade, find out what the car is for this car. If you have to fund your vehicle, you would also like to contact a bank / lender or two to find out what interest they were on that type of car. With this information in mind, check out all the dealerships in your area to determine which dealers have the car you want in the color you want with the options you want. There may be one vendor or several. Go down to these commissions advertise the best price for the car and drive it. Do not dispute how much down payment you have, what kind of payment you want, whether you have a business or not. If this car is acceptable, negotiations start.
You are trying to get the price as low as possible and understand that they will not go under what they have invested in the car, which is probably something a little more than the commercial value of the car. When I buy a car, I usually aim for a price somewhere between the average retail and average transaction prices. If it's a particularly clean car with very little miles, you may have to pay full retail, but it's probably worth it! The physical appearance of the car can and reflects how much the owner cares for his car!
If possible, ask that you speak to the decision maker. The seller may or may not negotiate the price of the car. If you are able to talk with sales managers, they are more likely to play the negotiation and are more likely to get into the "bottom" than the salesman, who is probably paid according to how much he sells the car.
Once you have negotiated a fair price for the car you buy and your business, your job is not over! Now you have to talk to a "finance manager" who is working to help you get a loan. Many times they can get a lot of growth for you, but they can also spread, so as to grow interest rates as well. If he can not relax the bank's interest, do not be afraid to tell him that you will return with bankruptcy from your bank. Also, if you make funding in the commission, be sure to print fine. I do not say you have to read every word of the contract but make sure that every form is, be aware of all the information that dealers have filled in and do not be afraid to ask questions if you are unsure of something! I really hope this helps. Good luck