I've heard that in some places, using certain nicety phrases in the contexts we would consider normal would be for them rude or strange. Do you check these or just assume the best?
I try to. For example pointing with the index finger is considered very rude in some places. I do my research but I am sure I screw up all the time. My favorite example of screwing up is when I went to France as a teenager. Several times when heading to the train station and getting lost I would ask people where the train station was by saying "Ou est la gare". (Where is the train station. Pronounced Gar) No one said anything the first several times but it turned out with my pronunciation I was actually asking "Where is the war?" (Pronounced Guerre).
I don't know about that in terms of day-to-day interactions, but I know that in service industries, U.S. politeness seems quite rude to Australians, while our version would be equally rude to them. It took me a long time to realise that U.S. customers weren't EXACTLY being rude to me, they were simply interacting in the way that they're accustomed to. They must have found me equally offensive. We try to be polite through relationship-building (chatter, making jokes, even teasing!). If one wants to be rude, it's done through distancing oneself ("You are not worth my attention as a person") even if the language forms used are perfectly courteous. To other nations, us being polite can appear pushy and extremely rude, assuming a relationship where there is no reason for one to exist.