when it comes to used cars, IMO, there is no such thing. I know what you're going through because I went through the exact same thing. I found a deal in NY, it was the car I was looking for (I specifically wanted an IS250 AWD with Nav + LUXURY package - its a rare combo). Two days before the dealer was going to sell me the car, he found a local person.
I was totally devastated as I thought it was a hard deal to find as I managed to negotiate it from $34500 to $32500. It also had only 8.5k miles on it. Well I then decided that I'll just wait ... combing autotrader during my free time - two weeks later, I found my car :-) and to make it sweeter, it had less 3k miles and $1000 less than I was willing to fork out.
If I come across a deal - I'll let you know :-)
Its a fun thing for me - I like looking for the best prices but cars are a hairy thing...