In a recent experiment, American cinnamon roll-specialist Cinnabon found that putting the ovens in the back of the store, thus not having the customers near the source of smell, had an incredibly negative effect on sales. As the smell of warm sugar and spices lingers, so do customers. Similar cases have caused retailers to focus more on the mostly neglected sense of smell, with some advertising agencies even specialising in this domain.
And while the research is not conclusive, the idea is clear. Smelling something pleasant can make you want to stay in a place longer, relax you enough to make decisions on impulse, and even get you to come back in the future. There are of course some difficulties. The aroma has to be strong enough to lure in customers from off the street, without causing inconvenience to neighbours. Combine this with the knowledge that one's sweet odour is another person's stench, and it's obvious using this tactic can be quite a challenge.
Abercrombie and Fitch claims their clientele is attracted to the scent they would wear themselves, so their stores always have the same musky perfume in the air. Some companies go as far as trying to brand themselves with a certain smell, like Singapore Airlines with the specially designed the aroma 'Stefan Floridian Waters'. Since its implementation it has been put in the perfumes of attendants, on the hot towels served during flight, and is of course always lightly circulated through the cabin of the plane.
This last one is a little less sneaky. In 2012 potato-foods manufacturer McCain launched a campaign in bus shelters in the UK. The poster had a large three dimensional potato replica for people to touch and feel, as a promotion for their new product. The claim was that their special ready-in-five-minutes jacket potato was just as good as a slowly baked old-fashioned one. So by pressing the button, the potato would quickly warm up, accompanied by the familiar smell. One that took three months to develop, by the way.