If the driver pays the lumper, the receipt has to come back with the POD.
November warehouses add lumpers and appointment fees for the holiday push. Somebody pays that bill. If it is the driver, you owe the driver. If it is the shipper, the shipper needs the receipt or they will not pay it.
Write it on the rate confirmation
Say who pays the lumper, what the cap is, and that the receipt comes back with the paperwork. A driver should not be floating a warehouse charge because the confirmation was silent.
No receipt, no bill to the customer. Do not ask the carrier to remember the amount a week later.