And read lots of blurbs for other books in your genre. The big trad publishers have some experience in blurb writing, one assumes. Look at what they do, analyze, see what works, and try to replicate.
The trouble with hiring someone is that they don't know your book, so either they have to read it, or you have to create a brief for them, not only telling them what the story is about, but also the mood etc. Creating a good brief takes time.
However, I do find it useful to run my blurb by someone who has read my book -- a trusted beta reader who knows the genre and can say whether or not you've captured the awesomeness of your book and whether they, as a reader, would pick it up.