Hide "Add to Cart" button when service is sold out and add a waitlist option on pages

Hello! 

I have read through many forums, but can't seeM to find the answer. Does anyone know how to hide the "add to cart" button on pages when a service is out of stock? 

Even better, does anyone know how to add a waitlist option on pages for sold out services? 

http://www.streettheatre.co.uk/feedbackpro (password is STteam)

Thank you!!

Have you checked this post?