I used to obsess about tipping as well: I kept forgetting the special customs of countries, and usually ended up giving way more than what was expected or nothing at all (by mistake, mostly). It's worth noting that in some countries the tipping process also varies regionally or even from restaurant to restaurant.

Now that I'm older and more callous I have simplified the process. I look at the receipt to check if there is a tip already included. If it is, we're done. Sure, I had discussions with waiters who insisted this is the bare minimum and I have to give something extra on top of that but now I simply leave and never go to that place again. If the tip isn't on the receipt, they get 10-20% depending on the quality of service. So far, this works well in every country.

I believe foreigners get a lot of abuse and are sometimes scammed by obnoxious staff who like to take advantage of the cultural insecurities of visitors. In my opinion, a good strategy is to always be friendly, but don't let yourself get bullied.

> Pizza delivery? What? Cab drivers? Seriously? The omelet chef in a hotel's breakfast restaurant? Are you kidding me?!?

I'm a native, but don't think it's so obvious for us either. One time I got a stern talking to by my barber. I now tip every time I get a haircut.

I used to work installing audio and video equipment as a kid and got tipped all the time.

If somebody renders any kind of service, tips are frequently expected.

Those guys are "porters" and essentially make their money from tips. I always just drag my gear inside.