Who charges $500 for a coolant swap? Who has ever gotten a coolant swap/flush done!? Is it a thing on these Volts?Did he do the regular maintenance on a timely basis? If, upon purchase, you have to put another $500 into coolant swap, $50 for an oil change, and $500 for new tires, the price may not be low enough. When you say it's "loaded", does that mean NAV? Ahy explanation as to why this 6 yr-old car is looking for its 3rd owner?
As for a replacement battery or section, you'd have to fight for that, and I'm doubting you'd be successful right now unless there are codes indicating a problem.