The most common thing that would make you quickly realize that it is high time that you got your carpet deep cleaned by an expert service provider is the presence of an odor that seems rather odd and out of place at any given point in time. Carpets can develop odors due to all kinds of factors, but the strange thing to remember here is that sometimes they can smell bad after carpet cleaning even if they smelled perfectly fine before it was done in some way, shape or form.
A big part of the reason why that is the case has to do with the fact that a Humble carpet cleaner often uses steam to remove dirt by dissolving it and sucking it up. This method is certainly useful, but it also makes your carpet wet enough that certain microbial organisms might try to settle down within its still moist fibers. Suffice it to say that carpets smelling bad after cleaning is not as uncommon as you might think, and it usually occurs because the carpet in question was not given enough time to dry before it started getting used again.
If you made the mistake of walking on your carpet while it still contained some moisture, the best thing to do is to just steam clean it again and lock the room so that you don’t make the same error repeatedly. You can also try using some fabric softener, but steam extraction will still be the necessary final step because unwashed surfactants can create slick and dirt attracting layers on your rug that will make matters even worse in more ways than one.