Because this is what I do for a living, please consider my response to be biassed. I wouldn't say you should or shouldn't do it; it all depends on your expectations. If you want to advertise a novel that you wrote in a month, for example, it's not the same as promoting a Roma work that took five years or more.
In comparison to the expected money from a simple novel book, hiring someone to do my job is not cheap. If this is the case, you should be able to handle it on your own.
I believe that a book, if taken seriously as a source of revenue, if not a life, should be treated as a company and that you should develop a business plan, taking into account expenditures as well as the value of well-designed promotion and design.
So, for example, if you book 2 dollars per month, hiring a pro will net you $5. It all depends on what the pro will ask and if you can cover the expense and provide an extra income. It also relies on the book's genre, target audience, and other factors. But, as is customary in Quota, this is getting into too much detail for a broad answer. Cheap essay writing services reviews.