It is not difficult to list a wrong item, if you are re-listing something like a t-shirt that you think still have some left, and then realise you do not have any yellow in size 12. 

It is lot more difficult to buy by accident; but then again i managed the other day and bought the wrong colour; as soon as I hit the "I commit" button I knew it was the wrong one.  Fortunately the seller was very nice and kindly switched it for the one I wanted.  It would have been more difficult if the colour I really wanted was from another seller.  🙂

But yes, it looks somewhat difficult to accidentally list a car.