First come first served? Not up to the driver

From the other perspective then I was running a goods in office and vehicles have a booking time, loose one at that and were tipped in order.
However once a couple of drivers just waited on the road and didn’t announce their arrival to us so I didn’t know about their arrival.
Next thing Stobart arrive, could have been anyone just as we finish tipping previous vehicle. So I tell Stobart to back up to doors and we’ll tip him now.
Suddenly there’s 2 drivers in my face shouting that they were next. My reply was that I didn’t even know they were here.
I made them wait.

sent using smoke signals