When you come to Lao Cai station for the night train from Hanoi from, step down door station will be a lot of people try to ask you to go and follow you. They will say there are bus Bac Ha, but its price is very expensive or no bus to Bac Ha … etc.
Things you need to do is to avoid them and go about your self the opposite side of the station about 200 meters will have bus stops. There you will find a bus going to Bac Ha for about $ 2.5 / person (60,000 VND). Do not pay any fees to anyone before the buses run at least 5km away from the city of Lao Cai.