The right solution will depend on having a clearer understanding of the goals of your directory and the needs of your users. But this is an area with many possible solutions:
http://www.wpmayor.com/best-directory-plugins-for-wordpress/
Review all of the above offerings (and any others you find) and compare their capabilities with your expectations. Evaluate them several times wearing different hats:
(a) the manager / owner of the marketplace: bulk populating listings, editing & moderation, seo, upgrades and payments, etc...
(b) a supply-side user of the market, i.e., an expert with a free listing as well as one with a premium listing, if applicable: creating, editing, ugrading, sharing and publicizing their listings etc.. Can they easily have multiple listings or locations, what fields are available to add details to their listings and do these prevent errors like mispelled categories and tags, etc...
(c) the end user looking for experts in various scenarios: casual browser, looking for a particular expert for the first time, returning user trying to do more advance actions like: saving experts for later, retrieving favorites, sharing an expert with someone else or on social media networks, contacting experts, rating or reviewing experts.
It is really important to also create a matrix of features and benefits for all the plugins you find and add qualitative evaluations of each. If you are not sure how to benchmark these start by looking outside of WordPress by looking at established marketplaces (in and out of your sector) to develop a list of criteria.
Finally, make sure the vendor of the plugin you choose is there for the long term, is well regarded by the community, and provides adequate documentation and support. Look at support forums closely, search for unanswered threads, view the change logs / development roadmaps, and contact the developers with pre sales questions.
