I was searching for an Emerald and saw the price at 8000, clicked Buy, and on the confirmation popup it still said 8000 so I confirmed and the purchase went through, however I ended up paying 9600.
My guess is that the one I wanted sold fast and I ended up paying for the next in line.
OR there is some exploit where someone can put a gem up for sale and continuosly change the price. I'm not sure I haven't tried it
Either way, if I'm confirming for 8k the system should not let me purchase it at 9.6k.