I have not found a way to ask this directly to facebook assistance because there is not an email address or chat/phone support.

I am testing facebook pixel event trigger on the ads control panel and I found that on every refresh a PageView event is triggered and on the thank you page a Purchase event too.
When the ads will be published officially, do facebook automatically recognize someone refresh the page and so will not charge me every time or I have to write some php code to avoid that?