How do you tell if a Wordpress template you bought was not copied or sold before?

So say, you buy a Wordpress template from a template designer who claims it is the only original template and that it was not copied/pirated and he has not sold to others before. How do you verify that you are only one with the original template? Are there any tools like copyscape that can check for copied Wordpress templates?

 

check for signatures, particular code in that template that may be indexed by a search engine

 

I search for oddball css style tags