I had a situation where my plane was fully fueled after which some friends showed up at the airport asking me to accompany me on my planned flight. The W&B was not working out with the additional weight and would require defueling the aircraft. The FBO wanted $0.95 per gallon to defuel and wouldn't credit the cost of said fuel. Can I ask the potential passengers to pay all defueling associated costs plus the cost of the lost fuel? Or, do I run afoul of the FARs?