Exporting/Importing a database for sharing with someone else or shared by someone else is not a feature of the addon, nor is it planned to be, as far as I'm aware.
I am a regular player which scanns the AH 2 times a day (before and after work) ;-) Me collegue is a player who play's 1-2 hours per week, but he would like to use AAdv with the same, "reliable" Database as i have. I would simply give him my db.
Or in case i would like to reinstall everything on my machine, i could backup my Database and start anything else from scratch. (No WoWecon is not an option...).
I know i could backup the db File in my WTF Subfolder, but not everybody knows this and if there would be an Export/Import Module, those players would not have to look for an AAdv db Backup/Restore function.
Sounds like a usefull feature to me. I am a bit surprised that such a feature is not on the ToDo list.
addons do not have any ability to perform file IO, which would be the traditional method of import/export. Other addons that do import/export typically do so by using long text strings you copy and paste. Given the amount of data we have (megabytes worth), there is no possible way for us to do this, even if we wanted to.
data could be exchanged in-game, but again, given the volumes involved, and the limits blizzard places on you before it disconnects you, doing this sort of exchange for a full database might take a long, long time. And it opens up security issues.
Given these issues, and the fact that you can in fact make manual backups to protect against machine changes, we have not chosen to explore any further.