Do the business halachos of ona’ah also pertain to non-Jews? Can one open up shop in a non-Jewish area and sell ones goods for more than the market value?
Technically there is no prohibition to overcharge a gentile. However in most instances the issue is merely technical, because in most cases of overcharging, there is an element of fooling ( or stealing) from the other person, which may not be done to a gentile.
As a side point from a practical standpoint it isn’t a smart thing to do, because eventually the customers will see that you are overcharging, and take their business somewhere else. Aside from this, you must be very careful not to make a chillul H-shem, because the gentiles will look at Jews as being crooks.
CH:M 348-2, Shulchan Aruch Horav Hilchos Onaah Ugneivas Daas1 &11, Pischei Choshen 5 chap. 10-1 ftnt. 2.