Second hand iPhone Troubles?

I bought a second hand iPhone from eBay, but it previously belonged to someone else. The phone is linked to the Apple ID of the old owner and I don't know it. Is there a way for me to still use the phone?

Yes. You will need a computer with iTunes installed on it. This will delete everything on the phone but will keep the phone number that is active on the phone right now. Plug the phone into the computer via the USB cable. Make sure the phone is turned off. Now hold down the home button and the power button for a good 30 seconds. A screen with a USB cable and an iTunes logo will apear on the iPhone. The computer will then recognize the phone and will give an option to restore iPhone. You will want to follow through with the restore process. The software will gued you through the steps and the entire process will take anywhere from 15-35 minutes to complete.

Then you can't use it, its as simple as that. The old owner needs to reset his own password and wipe it first.

If it's running iOS 6 and up (to 8) and has "Find My iPhone" turned on under iCloud (Settings>iCloud>Scroll down until you see 'Find My iPhone'), then NO- there's nothing you can do. Even if you did what was advised by Connor, it is still linked as a security measure (as if someone stole the phone trying to restore it). I know all this because I'm a Manager at an Apple Store.

At this point, you need to contact the seller and ask them to log onto iCloud, go to the Find My iPhone section, and tell them to remove the iPhone from their account. This will allow you to continue the activation.

If the seller refuses, or doesn't contact you, then you are out of luck because either it's a lost or stolen phone and there's nothing you can do.

Be careful next time.

There's no way to use it without the password. That's one of the many disadvantages of buying a stolen phone.