If you are sold a locked phone Apple will not assist you unlocking the the device, EVER.
The phone will be useless, a brick, it will be not anything you can ever use.
There is no "workaround" or "reset" to remove the lock. It is permanent.
You need to return the phone, it will and can never be unlocked by anyone but the original owner and if the owner bought it used then even he can not remove the lock if he forgot it..
If the deal is too good to be true, it's proably too good to be true and it's a scam.
eBay is not an authorized Apple retailer, the warranty on a new phone from eBay and Amazon being when the seller buys the phone from Apple, not when you buy from them, even if it's wrapped in the box, it does not matter and if you are sold a NEW phone from eBay or Amazon and it's locked Apple will not assist you unlocking this device under ANY circumstance.