In his hypothetical account of Flem's trip back to Frenchman's Bend, Gavin mentions why he could not ride with the "mail carrier," who takes passengers there "for a dollar" (305). Like other rural areas, Yoknapatawpha's Rural Free Delivery network employed multiple mailmen; this "carrier" is probably not the same person as the mail "rider" to delivers the mail to Whiteleaf and also charges a dollar for other services (176).
Unlike the other drivers in the novel, this one is imaginary. In his hypothetical account of Flem's trip to Frenchman's Bend in Chapter 17, Gavin describes the man who drives him as an outsider: his car "would not bear Yoknapatawpha County license plates" (305). (In Chapter 18, Ratliff describes how he himself drove Flem on that trip.)
In his hypothetical account of the deal Flem made with Eula that allowed Linda to leave home, Gavin assumes the presence of "two witnesses waiting" outside the room until she is ready to sign the agreement he has drawn up (304).
