Ok, I'm a dealer, so I think I can help a bit here, with your scores you can get better rates with a CU, cap-one and roadloans typically deal with secondary (less than 680 credit scores) and they will present a higher rate. Right now Chase Bank and Bank of America are buying every loan they can get there hands on and the rates are good, but check your CU's first.
Also, don't listen to anyone on here about a cars, thats a good deal on that car, I just did a Dealer KBB report on it, its the "real" Kelley Blue Book, not the one consumers see online and in books. A base 2006 Scion tC with 50K on it has a Retail Book Value of $16,015 and a wholesale book value (what you would hope to get one for at the auction) of $12,950, if its a Release 2.0 series, its worth even more. So $11,900 is a good deal, and if its the car you want then get it. 50,000 is a bit high, KBB considers 15,000 a year as average.
Pull a Carfax to check for recalls or accidents. And then check to see if its certified, most manufacturers offer "certified vehicles" on the used cars that are the same brand as what they sell new, so if its from a Toyota store they can certify it and the nice thing about that is that you'll usually have a small warranty (like 3 months, 3000 miles) to drive off with for peice of mind in case they forgot to inspect anything. Usually certified vehicles receive 110+ point inspections.
Also consider an extended warranty, but don't buy a off brand, or no-name warranty, like Vehicle One, they dont cover anything and those companies go out of business all the time. By a manufacturers brand warranty, a toyota, GM, Ford, for example, branded warranty so you'll be covered nationwide and it will be more comprehensive. They are a little more expensive but the off brand warranties are even worth your money, even if they're $700. If you have a good warranty you'll be fine with 50K on it.