Consumer grade carpet cleaners/extraction units are absolute garbage. You are lucky if you can get a years use out of the $100 - $200 level consumer units. They used to be okay but the new models are like 100% plastic and the brushes tend to seize up and have poor suction even after very moderate use.

The Bissell Big Green Professional Carpet Cleaner is the best unit you can get at a reasonable price that actually will last and works well (~$400). The Big Green is identical to the models that are for rent at hardware/grocery stores.