I sell an ozone treatment as an add on to my interior details. I will not ozone an interior unless I've detailed it first. Reason being the source of the odor needs to be removed or the ozone will just mask it temporarily.
It works amazing and definitely kills odors and leaves a fresh scent, think of the smell in the air just after a thunderstorm passes, just more potent. The scent will linger for a couple days but eventually clears out. I tell my customers to make sure to leave all the windows and doors open for a minimum one hour before entering the vehicle.
I believe they work by converting oxygen atoms (O2) into ozone (O3) through use of an electric current. I believe it's the same effect as lightning in the atmosphere (hence the similar scent as a thunderstorm). The ozone (O3) naturally converts back to oxygen (O2) and is completely harmless. Don't be mistaken though. ozone (O3) is not safe and you should not breathe it.
They work very well and can be picked up for relatively cheap. I believe I got mine for about $80 off amazon. I do recommend you do some google searching to educate yourself on them so you have the knowledge to explain to clients what the process really is and how it works and all.