"Qin" is a common chinese surname,also a dynasty of ancient China. The spelling accords with Pinyin, the modern phonetic symbols of chinese mandarin. This surname is spell as "Chin" in Taiwan. I am a chinese linguist as the informant.
Those who say this is pronounced "quin" are wrong. Q makes a hard "K" sound, never a "KW" sound. The "KW" sound is only possible if there is a "U" following the "Q". I am an English professor, from London, and can tell you the correct English pronunciation of the name is "kin". The correct Chinese pronunciation is "chin".