Couple of things...
Baking soda works great at sucking up stains on dirty carpet. As others have said, don't use a motorized brush to clean it up. I've found the soda gets on the belts and will cause slippage, which heats up the belt causing it to expand and ruining it.
As for stinky vac bags, remember, ideally we're cleaning up live bacteria, bugs, mites, moisture, dirt, etc. All that stuff, in a paper bag, left on a warm day, for weeks, etc. is bound to created stench as it grows.
I used to actively use my Electroluxs, both upright and Olympia. When ever the machines were not in use, I would carefully remove the bag and place it in a plastic shopping bag (or similar) and put it in the freezer.
Why? Because the freezing kills the bacteria.
And when it comes time to vacuum, put the bag in the machine and the smell is crisp and fresh. Like the smell one gets from a freezer where the fan is blowing the frozen air at you when you open the door.
Also, by not leaving the dirt in the machine, the machine stays clean. I would think the bags last longer because they aren't under threat of being consumed by the bacteria in the bag. In addition, for older metal machines, the moisture we pick up when vacuuming would stay in the bag and migrate into the machine, and cause rust. By removing the bag (and I always leave the bag doors open so the machine can ventilate), the moisture is removed, helping to preserve the vac.
