I am qualified to stick my oar in hear, as its what i do, and have done for many many years!
Actually the correct terminology is 'supporting Artists' thatswhat we LIKED to be called!
The days of 'equity' are LONG gone! There are 3 into which we fall regarding payment one is known as a 'walk on 1 '. Basic just crossing the road or standing in background the second is a 'walk on 2'. Ie: being dressed as a nurse/paramedic/policeman etc.....you get more for this and 3rd is a 'walk on 3' which is a speaking part, no matter how much or little you say.
The average wage is about £75 (in the North of England anyway)
We get told how to walk, how to pretend to talk etc.....some of them can be annoyingly OTT, but as most scenes would be unrealistic without us, you will just have to avert your eyes if we annoy you!
I am the opposite though, i am only watching the background, looking for friends.