PROFESSIONAL - Do I have to discount the appointments I post?

No, you do not have to discount, this is your choice and you have the option to include a discount to incentivise new clients, or reward existing clients for their flexibility in helping fill a last minute appointment which otherwise may go unfilled. 

On the search results page, appointment prices are shown along with details of any discounts offered, which may encourage new clients to book which will ultimately improve your revenue and business profits.