A question is asked about sexing fish and the OP is attacked?
As a new poster, I doubt I am going to fit in here if this is the norm!
Wuzi, there are several things to look for including but not limited to the midline ridge, firmness of abdomen, shape of the vent, shape of the pectoral fins.
Wuzi, Google "Sexing goldfish" you will find plenty of info on sexing your fish.