Search engines use backlinks as a ranking factor if the topics of the sites are related and the site providing the link is a high quality site, not one which sells links. Getting backlinks is difficult; you have to wait until people discover your great content, but they won't find your website if you are on page 10 of the SERPs. You write guest posts to get backlinks, but this takes a lot of time, especially when you need to write content for your own site.
Most people know not to cheat and buy backlinks from companies which sell them online. Google penalizes these companies and de-lists the blogs they use, leaving backlink buyers out-of-luck. Hiring freelancers seems like a better idea, especially if the person claims to get customers backlinks from authority websites. You'll find many freelancers on job boards offering to create backlinks from sites on Google News or other authority websites.
If you have a freelancer build you backlinks, find out what type of backlinks you'll receive. Will they be from directories, blog comments forum postings or contextual backlinks in articles? Ensure they are dofollow links, not no follow links.
Freelancers who get you quality backlinks from authoritative websites are expensive. When someone is too cheap, your likely to end up with links you have to disavow. When freelancers promise backlinks quickly, the links might be from a private blog network. They can only promise to post links immediately if they own the websites. It's true, you get what you pay for when hiring a freelancer.
This article is about freelancers, however, there is a small percentage of SEO firms that engage in black hat link building techniques as well. Any time you hire someone to perform SEO for you, you are putting your website's reputation with search engines in their hands. For more information click here https://www.reddit.com/r/SEO/comments/ca5vdo/freelancersclaimingbacklinksfromhigh/.