Situationally aware tipping in the USA like a decent person - how to ?
I continue my struggle to understand life in the United States of America.
I get restaurant situations, they spell it out for you after all, but am unsure what to do when nobody gives me my options expressed in percent on the bill.
Am I supposed to tip taxi drivers? If so, how much? I just booked an airport shuttle thing and it says 'gratuity is up to you' - I assume that means I am supposed to tip, but how much? Do I hand the person cash if I have prepaid the rest of the fare? (Nobody really seems to carry cash?) What about regular taxis?
I had my bicycle in a shop to get some things fixed and paid about 150$ for work and mostly parts. Everyone at the shop was really nice. At home I would expect a communal tip jar in a place like this and I would have thrown something in because they went out of their way, not because it would normally be expected. A six pack of beer or something along those lines would also be appropriate if they did something super special. Huge cash tips or just handing the guy some extra money would be weird and borderline insulting since they are professional bike mechanics and it would be like implying they need me to do them a charitable favour, like you would not tip, say, a car mechanic or a plumber either (right???) because this is a professional who is charging an appropriate amount for their time (right???).
The idea of trying to tip someone I'm not supposed to be tipping makes me feel way more awkward than undertipping (I don't want to do that either but that thought does not trigger the same level of cringe).
Can I get some general guidelines please?