Personally I am an Android user, but one thing I really love about iPhones is that, unless you physically damage the phone, they are almost impossible to brick. I have never heard of a bricked iPhone that could not be restored to factory settings via DFU. So most likely, your iPhone is recoverable.

You said you bought the phone from kijiji.com? What was the phone’s condition? Did it ever turn on normally? Get a flashlight and look inside the headphone jack. You should see a tiny paper strip. The strip should be 100% white. If it is orange, pink, or any other color other than white, then that means the phone has gotten wet, and you might indeed have a dead iPhone that needs major servicing. 

1002 means a hardware issue with the iPhone prevented iTunes from restoring. I had this error before, and basically what I did was just kept putting my iDevice in DFU, restoring, and repeating until eventually it accepted it. Apparently this worked for many people who asked me about the same error message. For me it took about 8 tries, it might take more, it might take less. Just know that you are more than likely to be able to fix the phone yourself.

I’m sorry, I can’t make out the last lines at all. Is that “Tried to jailbreak it with redsn0w ‘BY DOWNGRADING IT TO’ 4.2.1? Or is your firmware actually 4.2.1? Downgrading is a little complicated, and it involves adding IP addresses in the system files to trick iTunes into communicating with a server that tells it the firmware is legit. Its best to try to restore the iPhone to factory settings before jailbreaking it, so tell it to restore to the latest version of iOS, which should be 5.0.1 (which is still jailbreak-able). For now, do not use a firmware you downloaded from here or wherever you get firmware, just use the iOS iTunes provides for you. 

Keep us posted on your problem.