There is re-list option in form of extending ad expiry date. It is available once user logs in on ads page at the bottom in drop down select box. User can choose how many days they want to extend ad.
Classibase do not inform or send email to user when ad expires, also do not suggest re-listing. This feature may be added in next release. Issue with sending reminders is you have to send it once for not annoying users. We will think of this feature for making it right.