I think you did the right thing, Elke, and I'm sure it was appreciated by the server. Sometimes when in MIA shopping mall, I'll tip a cab driver $5 for a $3.50 ride (which would otherwise be a five minute deadly walk over busy lanes to get to my hotel, plus my shopping is heavy). He's lost his slot in the rank for a decent fare; I try to make up for it. Guilt? No ~ it's called mutual appreciation.