I know what it does (finding original content), but what I wish to know is if two pages are the same how is determined what is the original one ?
finding original content
"Verbatim" search has little to do with "finding original content". In fact, Verbatim search is just like an ordinary Google search except that Google will tend to use the exact keywords/phrases that you actually search for (as per the English definition of Verbatim, "in exactly the same words as were used originally"), rather than using it's heuristics engine to search for what it thinks you wanted to search for (keyword variations, synonyms, etc.)
So, the default ordering of the search results is the same, "relevance" (as determined by Google's internal - closely guarded, top secret - algorithms). This is regardless of whether you are using "Verbatim" search or not.