Fookin carpet cleaners, you're concerned about the wrong end. Those old skool machines are trash. They had their day, just like smoking and asbestos.
That day is over, today you should be concerned not just about agitation, and recovery but FILTRATION.
You should never go into a home or business and put more particles (dust, dirt, mold, skin, dander, hair) into the air stream.
The old machines were not designed to capture this stuff. The micon size of these particles is just too small to be filtered by a paper or cloth bag. you need a HEPA filter.
Now if you clean rat nasties, it may not matter to you. However if you are in nice homes they have been educated in recent years to HEPA filtration.
When you whip out some dinosaur of a vacuum you're telling that client you don't know or don't care about what you are doing to their indoor environment.
Don't be that guy, you may be inline for a scolding from them.