Easy work-around:
- the person trading to you must have 30k credits AND their own quest kiosk
- they set up a quest which nobody can solve without inside information; like, you must say "cmiiw gruben baden electric", as the first quest task, without any hints
- the prize for completing the quest would be 30k credits
- now, you can buy your own kiosk
VMK has stated that it "prefers" that the quests not be used for trading credits, but it's not against any rules.