I'm not sure where you live, but in the USA at a restaurant, the server takes your card, runs it in the PoS system, brings it back to you along with a receipt, and then you hand-write the tip amount on the receipt. Some of them bring a portable payment terminal to you, but it's the same idea.

When they give the receipt back to you for you to write the tip, the payment has already been authorized. It's already been sent to your bank, in a pending state, and your bank has replied saying the transaction will be approved. One of the receipts will have an authorization ID/number from your bank.

When you write the tip, they enter that into their PoS to modify the transaction amount, and finalize the transaction.

otherwise the waiter could just add in whatever tip they felt like and update the charge

That can actually happen. A lot of the time, issues like that are accidental (eg they typo the tip amount).

[–] emeralddawn45@lemmy.dbzer0.com 1 points 2 days ago (1 children)

That's a wild system. In Canada they bring the terminal to you, you put in the tip amount and then your card is charged all at once. Or at some places they'll bring you the bill and you can write in your tip, and then you take the bill up to a counter to pay. This only occurs in very small family restaurants usually though. Before chip and pin got popular they would still bring the bill and you would write in your tip, and then they'd take the bill and your card back and charge it all at once. Why would they take your card before you write in the tip, that doesn't even make sense and just creates an extra step.

[–] dan@upvote.au 1 points 2 days ago* (last edited 2 days ago)

Yeah, the USA is weird when it comes to banking and financial services.

Sounds like Canada is similar in Australia. At a lot of places in Australia, you pay when ordering. Sometimes you pay at the end. Aussies don't really do tips though, and prices must always include tax, so it's a lot simpler. Something on the menu is $20, you pay $20. That's it.