For me so far it has effected sales alot. Maybe that will improve over time but only time will tell. 

We of course ONLY list stock we have on hand but the problem arises if the item sells in our street shop and similtaneously on Ebay.....

Late shipping has a threshold of 5% but in the case of out of stock the threshold is ten times harsher at just 0.5% doesn't seem to make sense....