I use that offer on my leaflets, perhaps we need to look at the difference between a customer from a leaflet and a customer from a website.
some one who goes to your website has already decided they want thier carpet or suite cleaning they don't need a special offer to convince them
but someone who picks up a leaflet of the doorstep might never have thought about it, so a special offer might entice them to have some cleaning done.
special offers on website need to convince the customer to have additional work done, not the work that has prompted them to look at your website in the first place,
just my opinion.