You can sell the RLB that you get from the lootbox directly at rollbit casino, the features developed by rollbit are quite impressive and it seems they are pretty confident it won't make the price of this token drop deep enough due to massive dumping from the holder.
They have introduced this new development features few weeks back and manager have also shared the information about it which is great for the all the players and RLB holders as they can sell directly on Rollbit site and balance will be added to their account which they can later on withdraw easily making it more smooth experience for them.