These resale companies are churning contracts right and left. You absolutely do deal with a licensed real estate broker during the offer/counter offer process (it's the law), but once you sign on the line which is dotted, then the process moves over to a "concierge" team member, who is simply the paper pusher/facilitator of moving the process through the remaining steps. Calling them the "concierge" just makes you feel like you're getting some level of bespoke service, when it's actually just someone who would normally be referred to as an admin in most other office structures.