Comment by barbegal

I think the fact that out of stock items aren't shown isn't a UX improvement. If an item isn't in stock and you can't see that it is normally stocked then you will probably shift your business elsewhere and not come back. But even that wasn't the root cause of the issue here, the root cause was not making the user aware of the following logical fallacy: "if a single part exists for the vehicle only 1 part is shown" is not the same as "if 1 part is shown there only exists a single part for the vehicle".