It's funny if a tiler, a builder or plumber made a bags of something they would have to make good for free of charge. There are different procedure codes for every medical procedure carried out and some carry rules that prevent "repeat business". There are some procedures that are ever so slightly different also and are allowable though.
There are also rules in force where if surgery is carried out on multiple sites (the body that is), some insurers have a sliding scale of cover ranging from 100% to 50%.
Patrick