Studies have shown that the first impression of a home can be critical to the decision to buy. As little as the first five minutes can flip the mental switch between "Like / Don't Like" the home being shown by the realtor.
For many realtors, the ability to locate the right home is sheer economics. You can show ten homes or three homes. The impact on your time and resources is a fickle subject. Particularly when the first moments after entering potential buyer catch a whiff of some odd smell.
Vacant real estate can be worse than stale air from a closed-up home. Cooking smells from curry, fish, or ethnic cooking will persist for years. If past owners were smokers, the smoke odor has literally coated every surface. Carpet cleaning and new paint will not be enough to cancel those odors. Other bad smells are pet odors, mold and mildew smell, or just some odd smell that no one can figure out.
The solution is fairly simple. A good quality ozone generator can be used in the house for several hours as it sits vacant. Ozone adds no chemicals to the building. It is just enriched oxygen that reverts back to normal oxygen after treatment. However, the ozone will touch every surface neutralizing odors. If the furnace fan is allowed to run, ozone will even treat problems in the ducts.
Frankly, every office needs a couple of the 20G MAxx units from Professional Ozone. These very portable units can be placed into a vacant home for 3-4 hours to cancel foul odors after the building has been cleaned out. It is proper to do the cleaning, carpet cleaning, and remove property from the house. Treat with ozone as needed. Some will treat once the house is cleaned out, and again when all the preparation work has been done.
Ozone will do more than clear out odors. It will kill mold and mildew, reduce allergenic threats, and literally kill off any bacteria and virus in the house. Instead of the subtle "Lived In Smell", the house has a fresh smell that can make a big difference to any potential buyers walking in.