I’ve worked in two different bars in Europe, and they were both quite different so I’ll give you a little insight into how things work.
Normally, someone places an order, I go and make whatever it is they want, I bring it all in front of them, and then they pay. They leave and on I go to the next guy.
Really, in the end, it’s up to the bartender whether or not to open a tab. The owner might have an opinion that overrides this but it’s up to the man behind the bar to decide. In my first job I rarely did it, in my second we ran tabs all the time.
Many people would have thousand dollar bar-bills. Unless I was explicitly told not to let them add to it I would simply keep adding on to it.
Bars are sort of an old-fashioned business in this way. Or they can be. Obviously a chain-style bar won’t be doing this but a locally owned bar might depending on the clientele, and especially who you are!
That’s the thing. Locals. People that visit the bar often, or have done for a while. Locals will often get reduced prices, and believe it or not, there is usually a certain way to reduce the price on the register. Running a bar is based a lot on trust. I was lucky in that my boss trusted me. Whenever I made mistakes there was no suspicion. On the other hand i also worked for another boss who didn’t trust me. That sucked because every single mistake you made was a problem. I never stole anything FTR.
It’s a bit of a code, in a way. If you buy a drink, and don’t offer any money, and the bartender walks away, that means you have a tab. You might not even need to ask, but rest assured he’s got you remembered. If he brings you the drink, and waits on you, he’s expecting money. If you want a tab then, you have to ask. Of course he might say no, depending on whether he trusts you or management, etc. I usually asked for credit cards from people who I didn’t know.
On tipping. Yes you are expected to tip in the US. I believe the norm is usually ten percent. If you have a tab, you can add this at the end on the credit card receipt. You simply add it in the column. If you’re paying cash for each individual drink, pay with on extra dollar bill (assuming your drink is less than 5 dollars. In fact, if you buy a 5 dollar drink, and give the barman a 10, he’ll give you back five singles even if he has fives in the drawer.