When I travel on Amtrak with my dad, he gives the SCA a tip at the beginning. It has helped us arrange favorable terms for transition from sleeper to coach and vice versa when dealing with zone limits on Guest Rewards redemptions. There are also many occasions when an SCA, without negatively affecting any other passengers, can shuffle room assignments to keep groups together.
I, like a fool, give the tip at the end. I think my dad's method works better. I need to change.