My major requirement would be a better-than-average knowledge of the
OS and system mailer on the machine where LISTSERV is installed.  I spend
more time dealing with people who do not understand one or both of these
than I care to think about :)  If you have special needs for CGI scripting
or DBMS lists or so forth then of course your LISTSERV person should have
experience in those respective areas, or be able to draw on the resources
of other people in your organization for them.

The person in question should also have a reasonable level of communication
skills, if for no other reason than they will have to communicate with your
users and with support engineers.  All too often this seems to be overlooked
in the rush to find someone who has the technical skills to handle the job.

Nathan