[bret a ewing]

Yep,

The auction is set up in a "private Sale" manner.
The auction originator relies on personal email to continue the scam.

Ex: "I need to verify if you are serious about this car before I let you buy it. Email me personally and we will discuss arrangements." Or something to that effect.

Once enough prospective buyers make contact, the seller (scammer) ends the auction.
The seller now has a list of interested individuals with which to continue the scam.