The problem then is if you have a friend hold an off-camera flash while you snap a few pictures of another friend who may be dressed nicely you will have a ranger who thinks that person is a model and kick you out or fine you. You'll be kicked out faster too if the ranger hears your friend mention they'd like to buy one of those pictures from you. Someone posing for a portrait for their house/office is not a model, but I have met rangers who think just posing for a picture makes the person a model.
The problem then is if you have a friend hold an off-camera flash while you snap a few pictures of another friend who may be dressed nicely you will have a ranger who thinks that person is a model and kick you out or fine you. You'll be kicked out faster too if the ranger hears your friend mention they'd like to buy one of those pictures from you. Someone posing for a portrait for their house/office is not a model, but I have met rangers who think just posing for a picture makes the person a model.