On-sale vehicle sharing accessory device and system

A method comprising:

• receiving, in response to selection by a buyer, an access request for an on-sale vehicle;
• approving, via a vehicle-administration module, the access request;
• transmitting, in response to approving the access request, at least one authentication key to at least one of a portable wireless communication device and a plug-in device attached to the vehicle to enable vehicle access and vehicle operations for the on-sale vehicle by the buyer using the portable wireless communication device;
• confirming, in response to an access notification received by the administrative system, an identity of the buyer using a credential validation module;
• monitoring, via a driver-monitoring module, a test drive of the on-sale vehicle;
• and
• completing, upon conclusion of the test drive, a transaction by:
• revoking, in response to the buyer not purchasing the on-sale vehicle, the at least one authentication key, and
• revoking, in response to the buyer purchasing the on-sale vehicle, an authentication key of a prior titleholder.