To me it sounds like a right ball ache. Lets be honest, there are easier ways of acquiring customers than relying on them getting fed up of trying to do it themselves.
Plus, you will potentially lose out on £100 , £200, £300+ jobs when the customers lands on your site/see's you advert and see that you offer a rental at a fraction of the cost. Some will be cheapskates but there could be a lot of customers who may have been easily converted in to spending a bit more.
And lastly, I personally don't think it builds a good professional image if you also rent out a machine. Your basically saying anyone can do it. OR your going to do a bad job and possibly ruin your carpets but i'm still going to squeeze a bit out money out of you anyway.
p.s. delivery a machine back n forth to customers. Carrying this extra gear in your van while your doing proper jobs, then taking it out at the end of the day, then putting it all back in the next time a cheapskates fancies having a go... all for 50 quid....