As a former marketing contractor, I might be able to answer this properly. 🙂
I think it really depends on what you’re trying to achieve with said contract job.
“Digital marketing” is a very broad term and therefore you need to be more specific about your desired outcomes. One marketer might be really good at branding and design. Another at paid ads and demand generation. A third can organize events like no other.
I, personally, had to deal with a lot of vagueness in my own work as a freelancer. My expertise was marketing automation (which led me to end up working as Director of Revenue for marketing automation vendor Net-Results in Denver, Colorado).
In many cases, companies approached me with technical problems: “Can you help us implement this?”
More often than not, what I ran into was all kinds of problems that had nothing to do with the technical implementation – and everything with the strategy around the project. What is the desired outcome of the project? What is your marketing automation platform intended to do for you? Do you have a clear vision on your customer? Do you have great content?
So, more often than not, I wouldn’t even touch a marketing automation tool – and instead help the company focus on all those other matters before we could even think about implementation.
All that to illustrate that you, giving the assignment, need to be clear about what you want – and be ready to receive feedback from any freelancer worth their salt on whether that’s really what you need here.
So, make sure you set clear goals for your project. Then, think about which skills come into play. The contractor you should select should have some kind of proven skill – whether that’s LinkedIn recommendations and endorsements, actual case studies, Upwork reviews.
I do believe, as someone else here commented, that gut plays a role in this. Even if the person isn’t entirely perfect on paper, if you like their approach and the questions they ask (very important!), then clearly define a project scope and go for it.