People use all 5 senses when they visit a home for sale, and a great looking place can still put off a buyer if it has an unpleasant odour. Even if you eliminate major sources, you may be caught on short notice with a house that needs freshening due to paint or cooking smells. Opening windows may not be practical in bad weather, and traditional ideas like "baking cookies" require time.
A quick fix is to make a pot of coffee, or allow some to simmer on the stove. Add a little cinnamon or vanilla if you wish. Coffee is an excellent deodorizer: it absorbs, masks or removes many offensive smells. Used or fresh grounds also work in an open container, as do whole coffee beans (especially flavoured ones). Whole coffee beans are also decorative if displayed in a clear container.