Well this is really not a secret but it is a great idea I didn't think about prior to hearing about it through Paul Endress' Maximum Advantage.

Paul's focus is on discovering a persons core values so that you can focus on that to know what values drive their decisions.

One of the tips he shared which can trigger a persons historical values is probably the simplest one I've heard of.  I know there are agents or home owners that like to bake cookies in the over prior to an open house and that certainly can trigger memories for people and their childhoods.

This tip is even simpler.  Drip a couple drops on the stove with vanilla every hour or so and this will put of a calming and pleasing odor which will help trigger positive emotions with people when they walk through your house.