There are hundreds of companies world wide offering a myriad of services to the writer/author to help them get their work to the masses. The problem, unfortunately is there are also many of them who don't have the contacts to do the job as you may see fit or aren't astute enough to make correction or changes to your books.
So, what to do? Well, in my case it's weeks of sifting through internet pages for every thing I needed done to cherry pick who had the smarts, educational training, contact or whatever that would get me the most bang for the buck I was spending.
I implore you new and established authors (and this is a good reference point for the business entrepreneur also), to ask these on-line agencies and specialty places of business for some of their customer recommendations, and if possible, a contact name or something to ask them yourself what they thought of the services they were provided.
In cases of choosing book covers images there are illustrators who design original art for your covers and those who provide many choices and swap out parts of those cover images between others to form new cover art that they cane sell. Those non-specialized cover images are cheaper but, as I got from my publisher, will appear in someone else's book cover art in part on the web.
When choosing a editor or proofreader, well, in case you didn't already know, they're not the same thing. Although they people often seem to use the words interchangeably, one service is provided with more precise correction of punctuation, sentence structure, repetitiveness of your words/adjectives/nouns and etc. while the other is more of a check of the tone of your chapters and how readable and exciting they are to the reader.
Proofreading is the minimal and cost less while editing is more expensive and more in-depth. Be sure you question the person or company you are about to hire to make sure they do what you are expecting before you dish out any cash! Do you want them to move parts of a sentence around, say, from the end to the beginning to word it better, Do you need real help with semicolons vs. colon placement and other punctuation? What about reusing the same word over and over in a chapter. There is software available for that like Autocrit so check it out or send me a question and I'll try to help out as best as I can.
Stay up-to-date by joining my email list and reading more of my blogs too! Take care!
I'm very pleased that you came to visit my website. Feel free to contact me with questions and join the email list to stay up-to-date on news, top stories, writing tips and my schedule.