The truck at the dock has to be the truck on the rate confirmation.
Freight fraud is simple more often than people admit. Someone books the load under a real carrier's MC number, then a different truck shows up. If you load it, you may not see the freight again, and the carrier on the paperwork will tell you they never had it.
Match it before the doors close
Look up the carrier in SAFER and call the phone number on that record, not the number in the email. When the truck arrives, match the tractor and the trailer to what you were given. Take a picture of the truck number and the plates.
Stop the load if the broker tells the driver to use a different company name, if nobody will say where the freight is going, or if the rate is high enough that it does not make sense. A rushed just-load-it is how the freight leaves with the wrong truck.