Get It in Writing
Here's another way to make sure you're dealing with a legitimate carpet cleaner.
Ask for an estimate of work, and get a contract in writing that that is all that they are being hired to do, and all that you are paying them, based on their professional evaluation of your carpet cleaning needs.
This prevents conmen from later claiming that more work needs to be done, and later charging you extra for it, as some elderly folks in Devon learned the hard way. The carpet cleaner/conmen swindled some hefty £200,000 in total out of his customers.
Thankfully, he was caught and charged. And as it turned out, his business had gone bankrupt, too.
So if you're going to go into business as s professional carpet cleaner, make sure you deliver good service and that you treat your customers right.