When I worked at the construction site, my first six weeks of work were unofficial, and so the payment to me wasn't declared anywhere (probably ascribed to buying a bit more materials); as such, I received what's called "black payment" (which is analogous in meaning to black market, with "white payment" being taxed over and "grey payment" being a combination of two - so you might make 80k in total, but the organization only pays taxes on the officially declared 30k).

We would call black payment "paying under the table" here in the US. I don't think we have a name for the other two, but many places with cash tips are the same as your grey payment. Credit card tips are recorded, but sometimes it's up to the person being tipped to declare cash tips to be taxed.

This is one thing I love about English: you can address any man by using the respectful but not poetic "sir", and any(?) woman - by using "ma'am".

Yep! Tacking on a "sir" or "ma'am" is usually smiled upon. You can call an older man "sir" and be seen as respectful, while calling a younger man "sir" helps them feel respected and included. I've seen some younger women turn their nose up at being called ma'am because it makes them feel old, but everyone gets a healthy dose of "sir" and "ma'am" from me anyway. Take my respect, dammit!