In England at least, amateur detectorists are permitted to search on land not otherwise scheduled as ancient monuments, so long as the landowner's permission is sought and granted. Inevitably, over the course of many years, such activity will yield a haul of artefacts which are of such little intrinsic value or historical significance that they need not be reported to the relevant authorities (there are laws governing this). In the case of my friend, his collection had reached a point where he decided he would dispose of some of the lesser items via a dealer...yorkantiquities. So finder and retailer are not one and the same, nor is my friend the sole source of yorkantiquities' stock.