I don't know what reference I can give to EBS / BAF (bunker adjustment factor) which is more commonly used and understood ,it's part of the freight it's been like that since the year dot.
To put in very simply terms if a buyer appoints a trucker to collect some cargo from you
under FCA Seller's Premises,you load the truck but then the driver demands on the seller
pay him 100 dollars to pay for his fuel otherwise he won't deliver your cargo and also will not allow the seller to unload the cargo ....what would you do..call the police. .