Don't let courier guy take your package

I would rate them 0, I sell online via bobshop, sold to a buyer an Apple IMAC, it ended up at the client with the entire screen broken, the box has a gaping hole by the side piece of the box even missing, upon investigation they stated its not their fault as the item was smaller inside than the box despite the box having fragile stickers on courier guy states it should have had do not stack stickers on. so they in their own words admitted that despite it being fragile they did not adhere to that because it did not mention not to stack... courier guy got paid for that but they don't care about it, if my parcel is in your possession its your responsibility otherwise you must not take my money or my business. I will also be taking this matter further with the consumer protection act