"Items" are what you make, do sell, buy, or buy and sell. Not Vehicle. For instance, Oil Change, or New tire, or Tire Repair or "Welding" service and "noninventory parts" you bought and will charge to the customer.
Customer:Job is Owner:VIN Info.
Then the work you do, the purchases you make, and the Charges, are all assigned as Customer:Job = Owner and then VIN.
You can tell that item has Rate on it = not tracking VIN. VIN is like name and address and phone = Info, not Sales or Purchases.
Open Help and search on Work With Items.
Please see my attachment.