I think the biggest issue with player made dungeons with spawner traps is the possibility of abuse just to kill players for fun. Like, setting up a shop that leads to a horde of angry elite wildstock or something.
The second biggest issue that affects us more right now is giving players rewards. If you set up a shop stand one person can take everything. If you set up a ticket or storage system you need to add the person as a friend to give them storage permissions or to physically trade.
I think the second issue is easier to solve first - a shop stand setting that only allows you to take or buy a certain amount of items per account as opposed to per character would do wonders for this.