Through my re-enactments I have met a few "detectorist's".
One of which is a member of a club and gets permission from the land owner and works sites that have no "known" archaeology. This gave him an even greater interest in history and he is studying for a doctorate in archaeology and he takes his detector on digs to find artifacts, mark them so that they can be excavated properly.
The other is what is called a nighthawk, he enters known sites at night and will dig up and sell anything of value. I know for a fact that he has found a bronze age bridle hanging, a knife pommell in silver of a celtic womans/goddess's head and a gold stator.
This guy will go out at least three nights a week he does not work but has allways got cash.
I have only found a stone age axe plus a few microliths and a bronze coin of 3ad romano-british, by keeping my eyes open.
dave