One of economists Milton Friedman's rules of economics is that there is no such thing as a free lunch. The same probably applies to coffee and even yogurt.
Of course, the right thing to do in response to this act of goodwill is to tip the person far more than you would have spent on the coffee in the first place.
Outside of the train station they've been giving away HUGE tubs of greek yogurt.....
I still haven't quite figured out what you're meant to do with a family sized tub of greek yogurt first thing in the morning.
So am I missing something? How did you get free coffee?