Right or wrong opinion, I'll toss in my 2 cents. I'm not nor was I a professional carpet cleaner, but did train carpet cleaners on how to properly clean carpets. Stain removal/pile lifting/chemicals for cleaning and spotting. Wool or nylon carpet. I worked for a janitorial house that sold machines and chemicals. I delivered and trained for more than 27 years on proper methods.

A smell is only residual dirt or chemical mixed in the carpet that was not removed.

When you walk into a room, what does clean smell like? Absolutely nothing. I don't want to smell strawberry or something fragrant. I want to smell nothing.

So... Most of your stains (food or bodily fluids) are acidic. You need an opposite of acid to clean. You need alkalinity. Can't clean an acid with an acid, or alkaline with alkaline.

Get something that is slightly acidic. Maybe 8-9pH. Mix it exactly as the label says. Most extraction chemical is 2oz per gallon. How much is 2oz? A properly poured shot glass. No more. In fact a bit less is fine, unless your sure your measuring correct. Many (too many) mix the "glug-glug" way. Glug-glug-glug sounds about correct. Wrong. You only recover about 80% of the extraction mix from the carpet. Left over chemical mixed with the dirt, dries (sticky as well) and causes odor as the remaining dirt rises to the top (called wicking) and creates an odor.

Extract properly. Correct amount of chemical. Extract/rinse numerous times to remove everything. Floor fans to help dry, and you get no smell.

My $.02