A few months ago, I purchased a MacBook Pro on ebay. The unit is still registered to the guy who sold it to me. I've tried numerous times to contact him to ask hime to unregister it, but so far, no luck. I'm screwed, right?
MacBook Pro, OS X Yosemite (10.10.4)
Once an Apple computer is registered, there's no way to unregister it.
You won't be able to have any warranty work done on a used Mac.
You may run into other issues as well > Changing ownership of a used Mac | Apple Support Communities
Yep. You can try erasing the machine completely and trying to install OS X from your App Store account, but if it complains that you aren't the registered owner then it won't let you install OS X so the computer becomes useless. Nowadays, if you buy on eBay there is a high probability the hardware is stolen. You need to be very careful. You may have a recovery chance through the eBay protection plan.
The person who registers a computer or other hardware can remove the registration when it is sold so that the subsequent owner can re-register under their name and ID.
Unless a used Mac still has warranty time left you can't get any warranty work anyway.
Cannot unregister a Macbook Pro
