What would prevent the Key Fob from working?

Bought a used 2005 G6 for cheap, needs some body work and a few other things like the door latch fixed, dome light, etc but it came with a key fob that doesn't work. I replaced the battery but still not working. Provided that it is coded to the car (I wonder because the key only fits in the ignition and not the door or trunk) is there anything that can prevent the fob from working? Drivers power door lock switch works, passengers doesn't. Curious what I can check before taking it to the dealer to program it and want to prevent a situation where it fails and I still have to pay for the time spent.