If they check the PNR they will see that the ticket has not been issued (there’s no ticket number) and thus you do not have the confirmed onward reservation. Similar to how “hold your price” works at the airlines which offer this service - you get a verifiable reservation but not a ticket number and its not a confirmed ticket.
The goal of “airport taxi mafia” is normally just to overcharge you, not to rob you. In a shady location an airport taxi would likely be safer than a street taxi.