Selke normally fills the orders. However, if a file (typically a map) is too fragile or too large, Selke cannot scan the file. In this case Fahcolor Buhler can do the order as they have a large scanner. They are more expensive (my last order was ~50 Euro/map), so you want to make sure that Selke cannot do it, before ordering from Buhler.
My own experiences are that BAMA or Selke does not know ahead of time if they can do a file or not - typically the invoice will come with a note saying "we counldnt do xxx"