Viirkokka (how do you pronounce that?),
Just to set things straight, as some posts could be interpreted as being negative, I think I speak for all the mods here when I say that we do appreciate the input and suggestions.
As suggested earlier, when all items in a sale thread are gone, the person doing the selling can hit the report button or send us an email. Many people do this, I get plenty of email that way, many people don't bother. I think that a big shiny button would encourage more people to inform us of the end of their sale (but not all, as many people are lazy), so in that sense your idea is not a bad one. I do fear that it may well be a bitchingly large tech job to get that done... Still, you got me thinking.
Thanks for thinking along with us!