There's been alot of MMR exploiting in RBGs lately and I didn't see a thread on here so I decided to throw one up.
Apparently it works almost exactly the same as the arena MMR exploit did - as soon as a queue pops the "losing" team alt+f4s to avoid any MMR loss. The biggest difference between this bug and the arena one is that teams can use an offline member to ensure that they get matched with the teams they want to hit.
The match finding method is basically explained in this MMOwned thread :
Remove the (dot)s if you're interested in seeing the thread.
If both teams wait ~8m, they're almost gauranteed to queue into one another. The losing team then gives the other team a free win and so on. That thread also has 45 pages, mostly of people arranging win trading groups with each other.