There are several backend scripts which would be running if this were a real website.
The most obvious area where the database will need to be cleaned up is deleting the records of auctions that have already happened. This can occur automatically as part of a nightly or weekly cron job.
A more subtle area that will require cleanup is that of Auctioneers and their locations that have gone out of business or stopped using this service for some reason. Both the Auctioneer and Location tables have LastUsed dates that can be useful. The Auction cleanup script can be configured to automatically delete Auctioneer and Location records that are older than say 6 months, or could just send email to the site administrator noting the fact and leave any actions up to them.
The Registration page needs to have a backend script written for it that will send the email out on a weekly basis. Once the site gains a large number of registered users, (more than 3000 or so) this will require some speed optimization for the email task to finish in a single night. There are several different email list management packages to deal with this. The better ones can send out email in the range of ~50,000/hour. Also, the choice of right ISP is important because many will not allow such a large amount of email to originate from their service for fear of being labeled a SPAM house.
As with any large email system, there needs to be some method of handling bounces, unsubscribes, and incorrect email addresses in the system. Anecdotal evidence suggests that the email addresses will go bad at a rate of 20% each quarter. If your site becomes very popular, say 10000 registered users, then that means each week there will be about 150 newly broken email addresses. Scripts can be setup to automatically handle these bad email addresses. A common technique is to delete the user from the database after 4 weeks of bounced email.
Depending on the auctioneer demographics, a weekly hitcount could be emailed out to the auctioneers who have online accounts. This would assist in proving the worth of the site to them and justifying any future cost increases. It's best to wait until the site is getting significant traffic before starting this feature up.
Once the number of auctions in the database starts to grow, a good search page needs to be added. This would allow the users to look for auctions based on the date, distance and catagories, all at the same time.
This site is currently optimized for auctions occuring frequently as the same spots, as frequently happens with larger auction houses. However, in more rural settings, many auctions are estate sales held at the family homestead. There should be a one-shot location form to accomodate these auctions.