questions on upgrades n 'clean' weapons

hi ill like to ask if upgrades can be used on unclean weapons for example a blue icy longbow of fortitude. if they can then why is it that clean weapons r worth more?

You can apply any weapon upgrade to a weapon, the new upgrade will just override the old one. As for why clean weapons go for more. I don't think that they do. THey are in a little more demand because they should be cheaper then an upgraded one.

Well some collectors items cannot be salvaged, and therefore i suspect that an upgrade in it cannot be replaced. In a situation where people are buying a noncollectors sword, they often know exactly what upgrades they will want to put in the sword. So they dont really care if the sword has 10/5 Sundering, or 20 life fortitude upgrades in it already, cause they will be looking to replace them. If someone is selling a good sword cheap cause it has bad upgrades in them, then you have an chance at making a good deal.

Upgrades on collectors items can be replaced. They just can not be salvaged. And that is why no one really wants them. Plus most people just want the bragging rights of saying I have the perfect Bow/sword/whatever.