I have had to fly to Sydney and melbourne and have been getting taxis a lot, to and from airports. Last time the driver went to drive off with my laptop and wee case and I had to run after him
Talking to a work collegaue he said this happens alot - so if your stuff is in thye boot - dont close passenger door - keep it wide open until you have your belongings.
Or keep things with you at all times
Have to say though - this hapened in Sydney and not here