Credit is not only a way for consumers to extend their spending abilities; it's also used to judge financial responsibility -- all from information meticulously listed on credit reports. A February study from the Federal Trade Commission showed that 42 million Americans may have errors on their credit report. These errors cause unnecessary blemishes that result in lower credit scores, which means higher interest rates on mortgages and car loans -- all because of mistakes that are no fault of the consumer. "Look for derogatory marks, which can be missed payments, defaults, liens and garnishments," says Kenneth Lin, founder and CEO of CreditKarma.com. "These are the big uh-ohs and if not corrected, can cause your credit score to drop 100 to 200 points,"