Before you pay anyone, consider these FREE options:
Your university library likely has:
Literature search help — librarians can teach you to search PubMed/EMBASE effectively
Citation management support — EndNote/Zotero help
Systematic review consultations — for complex projects
Emory's Health Sciences Library has Informationists who provide "literature reviews and expert searches to support research proposals or grants" and "development of literature review strategies for thesis topics" . Many universities offer similar services. Check your library's website for "research consultations" or "subject librarians."
Also, the Health Sciences Writing Centre at University of Toronto offers personalized instruction (free for their students) . See if your school has something similar!