When working with an advertising specialist, if the employee is not on staff and hasn't had time to delve into all the features of the business, it is important to have an experienced specialist from the customer side (from management or marketing department). There are lots of businesses, and agency and freelance workers unless they ve d specialised in;the same industry over the years may not see the map and not include the nuances in the customer. Specialization of agencies and hires depends a lot on the number of customers in the industry and the amount of advertising budgets. More often there are specialists and agencies working with automobile subject, real estate subject, internet-shops. If your business is in a narrow niche, and advertising budgets in it usually is not a lot, it is not a real problem to find a specialist.
The best option in such cases will be a collaboration with a specialist in advertising. First of all it will help if the client will have a specialist at start by filling out the brief, answering his questions. And to make sure the advertising messages meet the expectations of your target audience, it's worth checking and coordinating the ads before the start