Finding the right marketing person will determine how much revenue you take in. This can lead to great success, or a total flop if the marketing & sales don't work.
Keeping that in mind, there's about 100 questions to consider for such a candidate, which you can find in the list of questions for cofounders or business partners.
I strongly recommend a phased approach to collaboration, with an initial trial period, and benefits or rewards coming only after proven results.
Ultimately, when you work with the person for at least a full year, you will know if they are "not a fit", just mediocre, or totally amazing for your business.
Feel free to DM if I can help further.