I send thank you 'emails'
After I thank them for their visit and tell them how much I enjoyed meeting them, I tell them that the best form of advertising comes from my guests and include a link to the Inn on TA. It reads something like this:
It is free and easy to register on TA, only a couple minutes. Make sure you let others know what you liked/didn't like in the area or the Inn. If there were any problems with your stay that went unaddressed, please don't hesitate to let me know. Future guests will thank you!