The process of hot-water extracting the textiles in question will effectively remove the source of the odor in all but the worst cases. In evaluating the level of deodorizing success to be expected, it helps to qualify the extent of the challenge. Is the problem an isolated one, such as a pet accident, or is it a continuing situation, such as a pet that is not litter-box trained or otherwise housebroken? The latter scenario presents a major challenge for the cleaner, one that may include removing and replacing pad/cushion and treating the carpet backing as well as subfloor.
If the odor to be corrected is sharp and ammonia-like, it is generally urine deposits causing the offensive odor. Heavy urine deposits will necessitate the pad/cushion treatments mentioned above. If you decide that addressing deep, heavy contamination is the type of deodorizing service you would like to offer, it highly recommended that you attend a good multi-day "Guaranteed Odor Control" class. There you will learn in depth about various deodorizers and their proper use. You should also learn which jobs to pass up.
If the odor is dull like a wet dog or garbage, it is often times topical - on the top of the carpet - and may very well be removed and corrected by a thorough hot-water rinse preceded by a treatment with a deodorizing pre-treatment. This type of treatment may be most closely compared to laundering dirty clothes or diapers to correct odor conditions. Many cleaners offer free deodorizing with their cleaning service and this type of odor situation (topical) is the sort that will be corrected or improved by a simple cleaning.
Be sure to qualify the job with the homeowner, letting them know if the problem that they have will not be corrected by the free deodorizing offer but will instead require disengaging and removing the carpet and any affected pad, as well as having the subfloor sealed. Using a rinse with an odor of its own will leave a little masking scent behind. Keep in mind that some customers are partial to specific scents, or may be turned off by any odor in the cleaning agent. My customers seem to prefer a citrus scent, which may be related to being located in the citrus capital of the country.
It is imperative that you inform your customer that unless the source of the odor is removed there is a very strong likelihood that the odor will return. You certainly cannot guarantee odor removal unless the source of the odor is removed or contained. In a nutshell, many odor problems will be corrected by just cleaning, while others will require major corrective steps involving various degree of labor being reflected in the price charged for the service.
I hope that these thoughts will help you in determining which types of odor situations you would like to address. Just remember to get it clean and get it dry!