I think it depends on the dialect. The Vietnamese who live in the north pronounce quite clearly every sound but we are sometimes confused between "s" and "x", "d" and "gi" and "r". The problem which you recommend here may happen to the Vietnamese ones who live in the center or in the south

n and ng have different pronounce. you will be understand when hearing.

we can best understand when we talk voice:)

it just like any other languages. Vnmese live in different area - north, centre, and south; so we have different accents. This sometimes leads to mistake in writting. for example, in the north of VN, they hardly distinguish between " L" and " N". So, instead of saying "làm ăn" , they say "nàm ăn". That's kind of thing. However, i think if you can guess the meaning in a particular circumstance, you will find out the right words.