Another scam, at the prepaid queue, a coolie (porter) or several appears and accompanies you to your taxi (I don't do checked luggage, and therefore I carry my own luggage, but this does not dissuade them). He touches the luggage after it has been put in the boot (either by the passenger or the driver) then aggressively demands a tip as the "taxi loader." I have witnessed these characters even getting into the back seat to berate unsuspecting travelers for tip money.
Resolution: get your driver to load the luggage and to lock the boot. Then lock all doors and instruct the driver to go.