qingdao to beijing train ticket prices

hello, i wanted to ask, how often are the train ticket prices changed from what is posted compared to the window. on 4/20 your site posted tickets from Qingdao to Beijing as 373 for a 2nd class seat. When I got to the window it was 474! needless to say that is a HUGE difference. what would be the reason the price would be so different? I am hesitant to trust this website now....