Maintenance light came on today on my newly purchased used 2012 Corolla sedan (not Sport model); why?

Why would you return the car, the car has preset Maintenance schedule. That light will come on a different milage...you need to get a copy of the owners manual. You can do the service or reset the maintenance light.

It runs good? cool- just do the maintenance- if you feel they should have done it before they sold it to you, then ask them- maybe they did- and maybe they will reset your light- good luck-

Turn the key 'on' and make sure the odometer is on total mileage, not TRIP 'A' or 'B' Turn key off. Press the button and hold it down. Turn key ON, or RUN position (do not start engine) and hold the button down and you can watch it count to 4 lines, 3, 2, 1 0. Release the button. The light will be off.

That light will appear every 5000 miles and is nothing more than an oil change reminder. Use 0W20 synthetic and change at no more than 10,000 miles, I change at 7500. and please for the sake of your car use a quality filter. yes, an expensive filter is worth every penny

https://ssl.toyota.com/owners/login

Get your VIN and register at the above link. You will have access to all service records done to your car at any Toyota dealer But you can't just 'return' it like a coffee-maker regardless, you signed a contract for a used car whether you paid cash or financed they are not just going to accept it back