Okay, thanks for the replies. Yes I do run to get a car (I even fell/slipped in the mud a few times), because I marshall like I want to be marshalled. But if I get there and it starts driving away from me, I'm not happy.
So I guess I'll keep chasing it down, but at a slower pace. No point getting further away from my marshalling spot when someone who does wait for me to get them might get stuck right?