Originally Posted by
televisor
Without evidence to the contrary I wouldn't assume that they'll return someone who is inadmissible as opposed to escorting them to the flight they already have tickets for. Your citizenship and residency of third countries might also play a part in this, especially if the onward flight is to your home country.
I think its generally CBPs policy to escort you onto a flight that is either your country of citizenship or a country you have the right to work/live in. On a recent flight I saw an Australian man being escorted onto a plane by CBP to Canada.
I can't see them sending people back to a country they are neither a citizen or work permit holder off, as the person could just get stuck of a loop of being sent backwards and forwards.