I don't know offhand about how to clear the data, but I know it can be done.

In regards to how often you should scan. For the first 2 weeks of a fresh data set, at least 3 times a day, morning, afternoon, and evening. This will give you a solid base set of data to work with.

After that you really should try to scan at least once a day. Sometimes the prices of items can double in as little as a week depending on events and patches. Or you may be missing that the gems your selling sell for twice as much on wed and thurs, meaning you can buy them on sat and sun and post them tues to make a killing.

Re: Clearing Auctioneer Data

/auc clear [itemlink] - this command will clear data for a specific item; very useful if an item suddenly increases or decrease in price. Obviously you need to perform new scans to obtain fresh data.

/auc clear all - this command should clear all data for your faction/realm. Alternatively there is a way you can delete Auc-Stat files from your .WTF directory, but you should probably consult the Auctioneer forums on how to do that:

http://forums.norganna.org/