I've been selling electronics in Greeley for 9 years. I test all of my units for full functionality before resale and yes the charge is included. Specs vary depending on what I have in stock because I am constantly selling and receiving new inventory.
These models are typically the Core 2 Duo Processor. Storage size is approximately 250GB of internal storage and yes some are 500GB. Yes I can upgrade this if you'd like to spend more. I also test the batteries for health. Ram size is anywhere from 2 to 8GB depending on what I have in stock.
Do I do upgrades? Of course. The unit must be purchased beforehand but I can install more ram, Solid state drives, larger hard drives, etc. I also do repairs as well.
What else do I sell? I sell many other Macs such as the airs, pros and yes, iMacs. Let me know what you're using the computer for and I can find that will fit you perfectly.