My husband is in a wheelchair because of MS, so we use the services of a pusher in U.S. airports. This service includes transferring him to an aisle chair to get on the plane and then placing him in the seat of the plane. The providers are employees of a service company (i.e., not airport or airline employees), so I assume they aren't being paid enough for their services and training (believe me, there are some truly incompetent fellows when it comes to transferring someone from one chair to another or into an airplane seat! Training in these things matters.). As a result, I will tip for the trip to the gate and for the transfer and will tip extra if we're brought to the car on arrival. $5 seems okay for an ordinary assist, or $10 for carside assistance. Yeah I know it shouldn't be necessary, but this is the U.S. we're talking about, where the custom is to underpay employees and assume they'll make it up with tips. I've never had one hang around hemming and hawing as if he's expecting a tip, but they always seem grateful when one is offered