SES light can be caused by pretty much anything from a loose fuel tank cap to a bad 02 sensor to bad coils. Have the dealer pull the code with an OBD scanner while you stand there. Write down the code and then look it up in the FAQ/How-to stickies up at the top of this forum. Then you will know what it is and we can help you from there and provide advice.
DO NOT let them just "clear the code" without proof they fixed the problem....it will come back eventually and they may not warranty the problem.
$8k is not a bad deal for a car with that mileage in decent condition. I still owe that much on my '00
and it has 10K more miles.
A few other suggestions:
1. take the engine cover off and check to see if the coils have a "dot" on them. If not, chances are they are the original coils and one or more may be bad.
2. if it has Bridgestone Potenza RE92 tires on it, make them either replace them or knock $500 off the price so you can replace them. Those things are DANGEROUS!
3. Drive it an listen closely for bad wheel bearings. At that mileage, it is not uncommon for the maxima's front bearing(s) to go bad.
4. Have an independent mechanic check everything out, unless the dealer is offering a warranty.