Originally Posted by
Qinshi
By Chinese, I assume your mother language is Mandarin. Therefore (as I am learning Mandarin incidentally) I will use pinyin to aid you.
Sạo
The letter s though technically should be pronounced a bit like sh, nowadays is becoming more and more like x in Vietnamese (s in pinyin). The vowel cluster ao is not like Mandarin ao, the a is pronounced like in cat whereas the Mandarin a is like in father. in fact, ao sounds like the sound in cow. The nặng tone (in Southern vietnamese) is practically the same as Mandarin third tone (第三声). So overall, it is pronounced like Mandarin sǎo where the a is soft like in cat, not hard like in father.
Xấu
Simply like pinyin sou and unlike 第二声, the sắc tone rises immediately, unlike in Mandarin where it dips slightly before rising.
Oh and I speak the Australian variety of English and Southern variety of Vietnamese so I understand my explanations may be a bit off.