Stop selling out of stock Items.

Stop selling out of stock Items.

Hi
I have been using Zohobooks for a around 8 month now. I am not involved in selling process but my staff cant stop selling product which they do not hold in stock, this is a big headache for me as physical count never matches what is shown on the books. 

is there a way to stop selling items which are out of stock?
you help would greatly be appreciated.

Thanks