Although there's nothing you can do about the matter if your item happens to get lobbed into the back of a van rather than being placed into the van carefully, there are steps you can take to minimise the chances of any delicate items from ending up getting damaged in transit.
Let's say for example that you've just sold that large French terracotta pot that you've currently got listed for sale at the time of typing this response. When you come to pack it up, use a double-walled cardboard box for maximum protection, making sure that you pack out the insides with polystyrene foam to absorb any knocks during transit, and fill up any remaining gaps around the pot with bubblewrap so as to prevent the item from moving around in transit. Just to be on the safe side, pack out the inside of the terracotta pot with bubblewrap as well.
Once you've finished packing out the parcel, tape it up tightly with the type of red and white tape that has the word "Fragile" printed across the tape in bold red letters so as to make it absolutely clear to the person handling the item that it needs to be handled with care. Although there is no guarantee that this will prevent the item from getting chucked around during transit, by attempting to make the packaging as bulletproof as possible and drawing attention to the fact that it is a fragile item, it should help to minimise the chances of the item getting damaged in transit, as the shock absorbing materials included in the box should help to absorb any heavy knocks that the parcel takes whilst in transit.
Finally, once you've found a courier you can trust check out the level of insurance available for all of their services and select the postage option that will provide you with the greatest amount of compensation in relation to the item's value in the event that something goes wrong and it does get smashed in transit.
