Have often been on regular commercial flights that have been refuelled with pax onboard. Usually there has been an announcment - pax told to ensure belts are unfastened, and crew members check the cabin throughout refuelling. Usually also an announcement when refuelling has completed.
I believe Australian and other international regs require F/A's and at least one tech crew to remain on board during the exercise to direct and assist in case of an emergency.