Your credit score is nothing more than an indication to the person who offers credit as to how well you have paid your debts in the past. It also considers your debt load, your balance to credit limit ratio and the length and depth of your credit profile.
Credit score is a mathematical formula that was invented by Fair Isaac Company that measures these factors and assigns you a credit score, much like a teacher issues a grade on your overall performance. More what's a good credit score.
However, it's entirely possible to have a 650 credit score and still qualify for excellent credit deals. This is based on the type of credit that you are applying for, your debt to income ratio, down payment and credit history. Meaning, if you are trying to buy a car and your credit score is 650, you can still qualify for an excellent credit interest rate depending on the mitigating factors.
Here's a good example. Let's assume you have a 650 credit score and you want to finance a $30,000 car. Your credit score could be low for something as simple as having a high balance on a credit card that you just put a vacation on.
Even though your credit score isn't that high, you have paid off several cars in the past without blemish and you are putting $5000 down on the car. Any banker in his or her right mind would jump at the prospect of giving you a loan. Some would try to charge you more interest for the lower score, but many wouldn't.
Having a low credit score hurts you if you cannot afford the car, or if you have a bad equity position in the car, or if you have missed payments in the past. But, if you CAN afford the car and you have paid your vehicle loans good in the past, there's no reason to settle for a higher rate. Shop around and you'll get a great rate.