Before you even think about going to the showroom, do you know how much you can truly afford?  Do a budget. You should have an Excel spreadsheet showing your income and expenses, including your car payments. If you don't know how much money you owe your creditors, you have a credit problem.

Credit Unions: There's one near you. They're set up for the benefit of members. Type 'your home town name credit union' into a search engine, and see what comes up.
Credit unions lend at better rates, but not as good as car financing web sites.

Before entering a dealer's lot you must get a copy of your credit report. Dealers know that almost everyone has a bad mark on their report, and they'll use it to charge you more. They may even lie about your credit score, saying it's lower than it actually is.

Fix any errors so they can't be used against you. If you have a good credit history, there is no reason to pay over 10%. Pay as much as you can in cash, get the basic model you need, and don't be persuaded to buy any extras. Running an automobile is a hideous expense these days; try not to increase it.

It's not an investment; cars depreciate in value immediately you buy them. Then there's tax, insurance, running and maintenance expenses. It's an emotional purchase, for most people, not rational.

Work with the right car financing professionals. There are thousands about. People think they must choose and stick with them no matter what. This is not so. Lenders and dealers work for you. If you are unhappy with one, fire them and get another.

Get disclosed writing how much your financing a car will cost including interest rate, trade-in value, taxes, and fees.

Companies offering financing for a car aren't charities. They're in business to make a profit, and only the simple-minded would begrudge them. So they add in fees and penalties and charges, either upfront, or into the interest rate.

They get lots of queries from people who haven't got the 'scratch' to repay a financing a car, so you can forgive them if they're a bit brusque; they've heard it all before.

Your financing request will be judged according to a formula, and any pleasant talk you get is merely them being eager and/or polite. If you can tick all the right boxes truthfully, you get a better deal; if not, a worse one. They're gambling on your ability to cover your debt, and your interest rate reflects the 'odds' of repayment.

This being a business deal, they'll try and get as much out of you as possible, but with the internet you can compare and contrast deals, and haggle a bit.

Have your money in the right spot. Be ready to buy. If you've got the moolah you can negotiate a deal, rather than wimping out saying you're 'waiting on financing' . No matter what, the money you need at completion should be available a few days ahead of time. This will ensure there is a smooth transaction.

Another way to winnow out the best company is to contact them via email, and see what they send you back. Call them on the 'phone as well. This, coupled with your impression of their site or offices, will give a good clue as to whether they're a 'sound', active company, or moribund i.e. on the way out of business. ALWAYS FOLLOW YOUR GUT REACTION. The mind has doubts, the heart has yearnings, but the intestines don't lie!