It must have been in the late 1980s or very early 1990s; my girlfriend and I were staying in Osuna in Spain. I wanted to visit Irni, where the Lex Irnitana had been found a couple of years before. We had already met a friendly man from Osuna, who had shown us some ancient finds from his land. We told him about our plan to go to Irni, and I think our host told someone that there were two people from Holland in town, interested in antiquities.
Not much later, while we were eating tapas in a restaurant, a young man asked permission to join us, and told us about his work: with a metal detector, he was searching for antiquities, and he sold them to foreigners. I asked him whether he did not feel guilty, but he said he did not; he had in the past told professional archaeologists about his finds, but they had taken his finds to Madrid. So, he had decided to sell his finds to foreigners. In both scenarios, the objects were lost for Osuna, but by selling them, at least something returned to the region: money. (“For yourself”, I thought.)
He offered his help if I wanted to purchase something, which I declined. Apparently, he concluded that we wanted to go to Irni to dig for ourselves, because next day, when we were there, we found the site guarded by someone with a gun, who continued to keep an eye on us, and cheerfully waved us goodbye when we left.
I mention this, because the argument of the young man has always impressed me. If you find something and decide to cooperate with professional archaeologists, and if your only reward is that they send it to another place, there is no stimulus to cooperate. This is why I think that small local museums, like Rindern and Haus Bürgel, are extremely important. They make people realize that the past is also theirs, and make them more willing to cooperate.