I used to own a shop and generally speaking if a person goes cheap on oil he will go cheap on everything else too. Why take a chance? Especially with an engine that would cost arm and a leg to repair if something goes wrong. It looks to me like you are getting a car that most likely had no maintenance done other than some mickey mouse stuff...I also agree with the nav being shit, btw the cd changer is shit too. I would get one without it, and go with garmin or motionx app for a smart phone which is even cheaper than garmin but with frequent updates and since it's on your phone you don't have to carry another contraption around...

Also, you will get a better deal by getting a car from a private party, you meet the owner and you can get a feel for the person and how much they cared for the car. A dealer will tell you what you want to hear...