Most malls are only promoted via search engines and random links and banners. Successful malls know that an offline promotion component is very essential. Ask specifically how the mall is promoted. If there are no offline plans, I'd go elsewhere. Find out how many visitors are visiting the malls home page each month.
Every server seems to count up hits in a different way.
Your concern should be the number of people visiting the home page. These represent potential buyers. You are paying the mall for the type of traffic they are drawing to their site. You want this to be shoppers, and if possible, representing the demographics of your typical buyer. I have found that most mall owners spend all their promotional efforts on attracting mall merchants.