Good to know that he's not a content writer
Paying a service before receiving it it's never a good idea. Still, from this perspective, an unpleasant discussion can arise: "I won't start without payment, what if I do the work and you don't pay me" vs. "I won't pay you for something you haven't done yet".
No matter on which side you are, I suggest going on recommendations, see who has the upvotes and is getting the good words.