Fair Isaac didn't start working on the idea of a quantitative credit scoring system until 1958, and didn't introduce its credit bureau scores until 1981.

That's right: banks used to lend people money without FICO scores. Instead they relied on stuff like employment history and, gasp, character. To get a loan, you used to have to meet with an officer or even a committee face to face, and they'd assess your reliability

As the foreclosure crisis has shown, relying solely on the quantitative can lead to disaster. The old-fashioned bankers might have been on to something. The Wall Street Journal reports (subscription required) that credit card issuers are now expanding their underwriting standards to include a focus on the applicant's line of work and where they live. If you work in construction in Nevada right now, you might have a tough time getting a loan.

This newfound prudence can be tough for some business owners who are seeing their lines of credit slashed for no reason other than that they're in a certain industry -- even if they happen to be faring quite well. But for most individual borrowers, I would say that a slash in your credit availability should be a warning sign that you're skating too close to the financial edge. The bank's metrics that tag you ask risky may be dead on, whether you realize it or not.

More about credit scoring:

Credit scoring myths

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We don't mean to get too personal, but what's your score? We're talking about your credit score, of course. A few years back, no one knew their credit score. Today, people brag (or complain) about it at cocktail parties and compare scores over the water cooler at work!

That's because knowing your credit score can have a huge impact on your wallet. Being a 640 versus a 690 means paying 12.2 percent versus 9.5 percent on your next loan, and that adds up to thousands of dollars in extra interest!

So, you already know that the higher your score the better. And you probably know the basics for keeping your score high-pay your bills on time, don't carry too much credit card debt, etc.. But you might be surprised at some little known factors that can do some serious damage to your score.

In a world where one delinquent payment-just one-can drop your score 100 points, let's look at eight credit score "no-no's" that pack a real wallop:

Do you want to pay down debt, but aren't sure how to do it? One of the best methods out there is called the snowball effect. This strategy of paying off debt focuses on getting rid of your highest interest rate credit cards first, which makes a lot of sense from a financial planning perspective because you reduce your interest expenses the fastest.

Think of the snowball effect as slowly building up the size of a your snowball then getting the snowball moving faster and faster by pushing it down hill. To use this strategy you start by paying the minimum amount on all but your highest interest credit card. Then use every extra cent you can find to pay the greatest amount you can on your highest interest credit card.

When you get that card paid off then continue paying the minimum amount you were paying on your second highest credit card plus the larger amount you were paying on the highest interest credit card.

Let me show you how this works. Suppose you have three credit cards that you've maxed out. Credit Card A charges 18% interest and has a balance of $1,000. Credit Card B charges 15% interest and has a balance of $2,000 with a minimum payment of $20. Credit Card C charges 12 percent and has a balance of $3,000 with a minimum payment of $35. In addition you have a car loan that charges 6% interest and a payment of $150 and a mortgage with a payment of $1,000.

Ken and Daria Dolan, America's First Family of Personal Finance, answer your questions every Friday.

Dear Ken and Daria,

I filed for bankruptcy and have recently gotten remarried. I wanted to know if my credit rating will hurt my new husband's credit. (He has excellent credit.) Thank you for your help!

Monica

Ken and Daria Dolan offer advice on debt management and living credit smart in their special report "8 Secrets Your Credit Card Company Doesn't Want You to Know," free from Dolans.com

Low-budget television ads and promotional websites are full of tricks for boosting your credit score.

A piece in the New York Times took a look at a few of these programs which, according to the Times, the strategies often "include piggy-backing onto a stranger's credit card and receiving pay stubs from a fake employer. The latest comes from a San Diego company, TradeLine Solutions, which claims it can improve a borrower's credit score by adding somebody else's top-notch credit history to the borrower's history."

But industry experts warn that many of the tactics for improving credit scores that seem to good to be true are -- and often, they border on fraud and could get you into serious trouble. Trying to use other people's good credit to improve your bad credit is definitely suspect, and the credit bureaus are working hard to crack down on it.

How do you know if a given method of improving your credit score is legit? Basically, anything that doesn't involve you behaving responsibly with your money is suspect.

And if you have a poor credit score, you may not even be doing yourself a favor using shortcuts to a better score: It'll just make it easier for you to get overextended again, in the same way that using a Sharpie to change the nutritional facts on the bag of Doritos is unlikely to help you get in shape.

To get in better financial shape by improving your credit score, check out Liz Pullman Weston's great book Your Credit Score.