How do you stop the merhcant changing currency?

The first time i sold a big item for ex by mistake i removed all small items from my stash. but now again i sold a item for 40 ex instead of div! i know its my fault, double check.. but everything i list is divs now why is it changing?

also is there actally nothing that can be done when you notice before the barraage of players comes to snipe?

you have idk 30 seconds or something to change your mind. in any case as far as i can tell it keeps whatever the last value i used was except for the first time i list something after logging in.