I like a Kirby for trashed apartments. They are powerful. I buy them used off Ebay for about $100. Only problem is they don't have a wand but they do get close to the wall. What they miss I just suck up with my vacuum hose.
I use a Pro Team 1500xp for most residential and commercial.
WINTERS !!!!!!!!!!! and April. 75% of customers in the HORRIBLE state of New Jersey wait till they are sure the cold and snow is done and after the cold and snow it rains 3-4-5 days a week in April. I'm totally dependent on nice weather to be busy. Most of my work is residential.
One possibility is.....They didn't use a CRB too get all the dog hair out of the carpet, especially the dog hair that's pushed down too the base of the carpet. The dog hair left in the carpet gets wet from cleaning and is causing that wet doggie odor. CRB is a must for these jobs.