The terminology here is probably worth explaining. Dealers, sometimes called Hucksters, take a space at the convention to sell their wares. Often these are books or comics or toys - things that the convention membership may be interested in but haven't seen in stores. There are two sorts of dealers: professionals, who sell things for a living, and fans, who may be at the convention to represent their club or organisation. Generally fans will get a considerable discount.
The Dealer/Huckster Liaison is responsible for sourcing and securing business for the Dealers Room at the convention as well as with the co-ordination of any associated sponsorship or out-of-con events (e.g. book signings). Naturally the DL will work closely with Publicity and the Guest Liaison in such matters.
The DL is responsible for approaching past and prospective Dealers, providing all rates and applicable information and, once business is secured, for ensuring that all Dealer needs are provided for and any pre-con problems are dealt with. The DL is also responsible for obtaining Dealer details and delivering these to the Treasurer in a timely manner so that invoices can be issued and payment chased up.
The DL is also responsible for ensuring the Dealers Room is appropriately set up when needed and securely locked when not in use. The DL should be in attendance at the beginning of the Convention to greet the Dealers upon arrival, escort them to the Dealers Room, advise of facilities and procedures, and troubleshoot if required.