It’s quite common in the US everywhere I’ve lived. Every tradesman I’ve used outside of large companies will offer a large discount for cash if you ask about it. They will likely not be the first to initiate though at a certain level of customer, since the social expectations change at a certain level of wealth.

This is almost always in a portion of the invoice written up at around half the agreed amount, and the rest in cash. Or for smaller jobs just on the side with no paperwork involved outside of a firm handshake.

This is the norm for the lower end of the trades. If you’re dealing with a single owner company with a few employees I’d be very surprised if they would not be willing.

Yeah, once you get into “real companies” that are charging upper middle class rates on million dollar properties it changes.

I haven’t had trades work done in Mexico, but considering all my visits were effectively cash only transactions I’d be pretty surprised if it wasn’t at least as common as in the US.

It's very common for small and independent businesses. You've likely never interacted with one.