Originally, when I had my carpet cleaned by Stanley Steemer in August 2015, I thought they did an ok job. I had just moved into my new house and there were various stains on the carpet that the old owners left. The technicians said that they couldn't remove the stains. They didn't really give me a reason and told me they were permanent. I didn't think much of it then because I didn't know any better.
Fast forward to now, I decided to try and get the stains out myself (with a much less powerful machine?, mind you) and had no problem... So what that tells me is that they were just lazy. The upsell was pretty ridiculous as well, so be prepared for that.