I live in Cape Town, a popular cruise ship destination. Over the summer, here, I used to work as a barman and waiter in my early 20s.
We (my colleagues and I) could recognise the nationality of people based purely on instinct and the dress that people used.
I had no idea about the ships in the harbour, even though I worked in restaurants in the habour, the cruise ship dock is not in view.
But we knew. We could identify Americans, English, Germans, Chinese (not that hard), Koreans, and more.
My aporoach was somewhat more profesional, but plenty of wait staff would steer guests into their own tables, or into soneone else’s section, based on looks, without even hearing an accent. Obviously a profit motive.
First, Americans. Tip really well, so a prize table. A bit talkative, so you need to be able to break off a conversation politely
Next Germans. Tip quite well, the only irritating thing is that each wants to split the bill and pay with their own card, which could lead to a lot of wasted time on international phone calls with their various banks to verify payments.
Chinese. Terrible tips, but they tend to spend inordinate amounts. I sold one table, probably illegally, 5 live giant Mozambique Crayfish - large lobster size - but the animals had large balls of eggs (berries) - so the tips were fine.
The English. They are terrible at home. I’ve worked service in London. But they read their guide book, and when it says, tipping is normally around 10%, by golly they will do that. Regardless of quality of service.
The Australians. Fuck the Australians. Minimum wage - which is what I was working for the time was a mere R5 an hour, AU$ 0.41 and US$ 0.27. I get that in their benighted country set about with all manner of animals who would really prefer the human population dead, their government has set an actual living minimum age, which keeps service staff alive, until they meet a salt water crocodile or box jellyfish or something.
A bit of a rant, I suppose, but yes, those of us who have a profit motive to quickly indentify nationality can certainly learn how to do so.