I hosted many GCAers during my years at Lake Merced, some on multiple occasions, and, except in one isolated instance, never asked anyone to pay a greens fee or any other cost of playing golf that day.
I've had a few reciprocations over the years, certainly not nearly as many as those I have hosted, but overall I would not change the way I approached it and treasure several non-hosted experiences that have come my way through my friendships at GCA.