I haven't heard about m-of-n transactions until now, but the way I understood it is that you do broadcast a transaction transferring the money to an account controlled by 2-of-3 people. So no one can then spend the money until two of the three people - the buyer, the seller, and the arbitrator - agree on what to do with it.
Does that create another way for money to just disappear? What happens if 2 people disagree and the other takes a flight to Conventry for whatever reason?
Yeah, it's important to have an arbitrator whom both parties trust to fulfill their obligation (such as a major bank, to borrow the article's example). Otherwise, the arbitrator could also just offer to split the money with one of the parties if the deal goes sour.
