Leaving the foriegn traders aside.... If as a trader your advertising something for sale then you already have it so you know what profit you want to make right So why not advertise the price ??? Only reason you wouldnt IMO is that you may think you can make more money out of some noob that just joined the scene rather than a seasoned modder...
Problem is I don't really blame them, I used to do it for the last company I worked for.... A trader comes in and gets bottom end price, man off street walks in and gets 50% mark up.... Thats life guys, as a buyer you make the decision to pay the money... if you research you can find out how much things are so your not forced into the transaction...
I agree with most though, if price isnt advertised it puts me off straight away... When members post in the for sale section we don't say pm me for price do we