[gtc]

I use a commercial carpet spotter so I don't know if you can do this with a cheapo bissel, but I usually boil a pot of water to use for the cleaning solution. It comes out hotter than hot tap water +25 degrees, or whatever the cheap bissel heated units put out.
When I do my porsche's fabric sport seats, I mist them with hot water to help loosen the dirt, spray with cleaner, scrub with reasonably soft brush, vacuum, spray water again to rinse, vacuum again, and repeat until clean. Afterwards I use 303 fabric protector to water/dirt/UV proof them.
The biggest difference between the cheap and the expensive units is the suction power and the construction of the vacuum heads, which allow you to press harder and get more water out of the upholstery.