I havnt read what everyone else has said, but its always the pilot decision...no matter what anyone says, too ****ing bad for the owner... I'll cancel a flight if I get allergies...
Your the one responsible, not him. So when something bad happens in flight, your in deep **** when the investigators find out you were 80lbs overweight.
Ive seen inspectors hand out safety and negligence fines over thousands of dollars to students who would take a c172 to do one or 2 take off landings in the pattern with full fuel and no one on board with no w/b data given for that flight.
Remember risk management is apart of our business ( IMSAFE, PAVE ), you should be able to spit it out if someone asks you what they stand for and how it relates to you.