My experience with PlugShare specifically was primarily with private residences. I emailed the home owners well ahead (more than a day), explaining that I would like to charge for a few hours, and the power draw (1200W for my 2014S), and received affirmative responses. At one home, the owner preferred that I ring the door when I arrived to plug in (to a 120V receptacle along the side of the house) but didn't require any compensation. At a different home. At a different home, the home owner did ask for modest compensation to be left in the mailbox, but to not ring when I arrived.
The one commercial property PlugShare I phoned (a restaurant) actually informed me that the PlugShare listed didn't exist, which was indirectly helpful as I would have had a hard time making the return trip and chose instead to drive a car.
Generally positive outcomes, but my PlugShare experience is that confirming access in advance is important.