I can't sign in with my Apple ID, It's asking for the former owners?
I purchased a used iPhone4s on EBay and I can't sign in with my AppleID, it is requesting the seller's email address?
iPhone 4S
You will need to contact them and have them remove the device from their iCloud account. If they cannot, or won't, then return the device for a refund. If the seller gives you any problems, then open a case with eBay. If they do not remove the device from their account, Activation Lock will prevent you from ever activating the phone. It will be useless to you.