Sue in California? How much is THAT going to cost someone based in Europe?
And really, what recourse does Fitness SF have either? If they sue him, maybe they win. Maybe that makes it hard for him to come to the USA. Is that a problem for him? Can they legitimately go after him vs his company (and vice versa). It's a no-win situation all around.
I'd say that the big lesson to be learned from this is that international customers pay up-front and with a deposit if you're going to allow things that increase the price (e.g. rush changes). For most things there's not usually a good reason to add the expense and complication of 12-hour time differences and international borders unless you're planning up front to make legal recourse difficult.