Moderating player generated content?

It's been noted that if you let players design content, they'll design set pieces which provide maximum reward for minimum effort. The reward might be in the form of achievements, xp, or loot. It would be impossible to get devs or trusted CMs to pre-emptively moderate player content, there would simply be too much of it.

What you could do though is deem that all un-moderated content will have zero rewards. No XP, no achievements, no loot. Players would have to play the content for the love of it, and if those players rate it highly then it's likely to be interesting content. "Interesting", as defined by devs. This highly rated content could then be slated for dev oversight and moderation, and rewards activated for that content.

Another idea is to have, at least, loot being dynamically determined. If endless gangs of adventurers are able to tramp on in and kill all the monsters, it's only reasonable to assume that their treasure chest will likely be bare. If on the other hand the monsters are snacking on a growing pile of adventurer corpses it would be reasonable to expect the mobs to have accumulated more treasure.