Non museum guides......
As you initially enter Auschwitz, some guys may approach you asking if you want a tour. Not sure if these guys are good or not. I have heard mixed reviews.......but you really do not need any guide at all inside Auschwitz I or II because its very self explanatory.
When you arrive in Oœwiêcim, on the road to the concentration camp, you will notice a parking with four or five people indicating you should park there.
Beware this is not the "official parking" of the State museum of Auschwitz! It is kind of abusive and costs 2.5 PLN an hour (for cars), while the parking of the museum has a fix fee of 7 PLN.
Unique Suggestions: You may consider parking in this "abusive parking" if you arrive in the late morning (let's say after 9 - 10), when the "official parking" is likely to be already full, due to the high amount of tourists come by car or autocar.
Fun Alternatives: If you are going to visit the concentration camp of Auschwitz, which will take you at least three or four hours, do not mind the signs of those young people and drive as far as the parking of the museum, which will be cheaper for you!
Watch out. Busfares are pretty cheap, about 8 zloty one-way. Many people try to strick you for their own deals in Krakau for 60 to 120 zloty return. They mention you get a return fare, free entrancy and transportation to between the 2 camps. The return fare is 16 zloty, entrance is free and transportation is free as well. So watch out! Also the tourguides can be bad, some only tell you what the signs say as well. So stick to an official tourguide.