I think it happens quite often that a beggar will beg for money for food but they have no real intention to buy food. One of my first encounters with a homeless person in SF when I moved back here was at Civic Center when Bart used to have a metro entrance/exit in front of the public library. There used to he a Burger King there also and a bunch of homeless people would hang out there and beg from the commuters. One guy came up to me asking for money to buy food but I actually didn't have any cash on me. I offered to buy him a Whopper meal but he said no and he'd rather have cash. Idk, maybe he had some sort of dietary restriction or he wanted booze or drugs.