One of my pet grips as a bookseller is when I go to a supplier and ask for a small quantity of items and they tell me, "We can't send those at the moment because we have a minimum order, and your order isn't big enough to qualify."
While it isn't the fault of the customer services person, she's usually the one who cops any complaint about this issue. But no amount of arguing avails - and if I insist on getting this pitifully small order from them, I am charged a small order charge. In the most recent instance, this was $10 - not a large sum, but enough to reduce my margin on the items.
I compare their approach to selling to mine: if I was to say to a customer walking in the door that they couldn't have what they wanted (say a $20 book) because it didn't fit my criterion of a minimum purchase, and that they had to buy another book - say at $30 - in order to walk out the door with the one they really wanted, well, I can imagine the kerfuffle.
Yet somehow this quite straightforward logic doesn't seem to occur to the supplier.
Contrast this to the suppliers who will send out books straightaway and will have them in your door the very next day - without even charging freight.