I didn't hire one, I bought one instead.
I got the Vax Rapide which is brilliant. I had a couple of stains that had been there for over a year (one being child vomit on a cream carpet), had tried everything to get them out. This got them out in one go.
I looked at hiring the Rug Doctor (think thats the name) & it worked out about £40-£50 to hire the thing for a day as you had to buy their carpet/upholstery cleaning solution which was about £15 each. The Vax was £180 (reduced from £270ish from Very), I could have got a cheaper one but I wanted one that could clean upholstery as well. I was potty training DS1 at the time so I decided I'd rather have one in the house to clean up "accidents"