I delivered a few samples of my cupcakes today. The only complaint was that the buttercream was crusty. I iced them the night before and put them the night before and put them in the box for delivery. How do i stop it from crusting? Or at least slow down the crust.  The recipe I use is:

1 stick of butter

230g powdered sugar

Pinch of salt

1/2tsp vanilla

Warm water, to desired consistency

The amount of fat/shortening/butter compared to the amount of sugar is what determines how much icing will crust or not   I suggest you check out the recipe “2  of everything “ found in the recipe section of this site   It can be made either crusting or not  

I really can't help with that because no matter how crusted my frosting is straight from the fridge, once it has been out for a while, it looses it's crust, much to my disgust!