The FMCSA has the rules for lumping who pays for it.

Haha... I know how you feel driver. Was this in Opelika, AL?

Te customer pays for it. I used to deliver paper pruducts to Sweet Paper in Hialeah Florida. The lumpers would knock at the door and charge high rates. Anywhere from $150 to $300 to unload the load. I would pay cash from my expence money, my boss would bill it back to the shipper, who would bill it back to the receiver. Finally Sweet Paper got wise to the fact that they were paying for it and started checking your paperwork, then they would say, "The lumper will get $80.00."
I tried to buck the system 30 years ago, I would hire a lumper that I wanted to hire, instead of taking the next guy in line, I don't like being told I have to deal with someone I don't want to deal with.
A few years ago I flew to Portland Maine to pick up a tractor for my local Freightliner dealer. His pilot dropped me at the FBO and I walked out the front door to get a cab. I walked to the third cab in line and told the driver I was going to the truck dealer. He told me, "You have to take the first cab in line."
I walked to the first cab and the driver was from the mideast, I told him, "I have six people at Signature Air that need cabs." He drove to Signature Air. I walked to the second cab in line and he too was from the mideast. I told him, "I have six people at Signature Air that need cabs." He drove to Signature Air. I walked to the third cab, got in and told him to take me to the truck dealer.