To pick up on some points:-
If a loco is sold as broken and then fixed, then I personally see no problem in selling. All reported problems (to which I doubt there will be any now!) would be dealt with individually, and I think that we could use our own heads in seeing someone who is clearly profiteering, or someone who has just decided to change eras or locations after a couple of months.
There is nothing I can do to stop anyone selling anything on other auction sites, as it's not illegal. However, the whole point of this is to keep with the ethos of the forum, by being a friendly community and helping each other. If someone does something to harm the community then they lose their privilege of being a member.
I appreciate the idea of a seller choosing whether a member can sell on the item or not. If members would like that then they can write that in their For Sale listings, or I could try and code something into the N'porium listings with a check box? Thoughts on that are welcome.