Actually, from what we've seen, there is. When Eleanor was trying to do good things for the other residents so that she could stay we saw that her selfish motivation meant that she wasn't actually earning any points. She only started earning points after she gave up on staying. And I think Janet provided that tracker, so it would make sense for it to run on genuine Good Place rules.
Jason did wonder if they'd been abducted by aliens, and he was right about it being a prank show, so...
That's true, I was thinking about the part where MIchael explains it to all of the new residents and couldn't recall him saying anything about intentions, but they do spell it out pretty clearly later. I also totally forgot Janet gave her the tracker.