I had a nice call last month from a local reporter doing a story about smells in a home for sale. It's a major concern in a lot of houses. Smells are one of the biggest turn offs for so many buyers and one of the things that home owners rarely address primarily because, well, they don't notice them.
Some obvious ones are cat boxes, baby diapers or stinky food. But some not so obvious (to the home owner, anyway) include air fresheners, especially those awful plug in kinds; mold or mildew smells; cigarette odors that are embedded in the walls or carpets; or that "old" smell that is really hard to pinpoint but must be addressed.
I was quoted several times, as were a few other local experts, and the general consensus is that clean wins over fake smells, and spending that time can help sell your house.
Here's a link to the article if you'd like to read it: That funky stink can sink home sale. Not sure how long the link will be active but it's from the November 13th Williamson A.M. portion of The Tennessean newspaper.