The "blue book" and other price guides are just that, suggestions--and as such, are meaningless, because every vehicle is different and each region of the country is different. You have to decide on what features you
1) must have
2) will not accept under no uncertain terms, and
3) would like to have but can live without.

Then look at the marketplace and to the regional data. With so many of these Car Max and Auto Nation sorts of places, you can find a decent used car these days, and you can do a search on each VIN to find out if the car has been in accidents, etc.

You can save a little money by buying directly from the original owner, and I've had good luck that way. But any purchase of a used vehicle can be a risk if you don't do your research.

Number one rule of car buying: Don't fall in love with the vehicle you're test driving, because you are no longer in a position to make an informed decision. Be a little stand-offish.

Good luck! You're doing the right thing--buying used cars is great for the pocketbook and great for the environment.

SRS