The "count member replies recieved" option at Admin Panel -> Settings -> Switches allows you to keep track of how often people comment on the listings of a member. It sums up the total number of comments on all the listings owned by the member, and makes that total available to display with {MEMBERREPLIESRECIEVED} wherever you want it (by default, it shows in the View Profile page).

Enabling this option slows down comment submissions slightly. The effect may become significant if you have hundreds of thousands of comments.