Marketing consultants can specialize in a variety of things. Some consultants specialize in advertising strategy, others in branding, and others in social media or website design.
However, the best marketing consultants specialize in strategy and making data-driven decisions. For example, marketing consultants specializing in a full-funnel approach can plan and execute a social media strategy that will affect your bottom line rather than just increasing your followers.
Once you have a formula that works and drives revenue for your organization, creating a cost-effective approach to execution is much easier.